Walls, floors etc in sims2pack format
When creators upload a TON of files without adding a big file with all packages in it, which would be a lot easier and save a lot of time. Please, it doesn't even take a minute.
Lipsticks with teeth
Skintones that are overly shiny, look greasy (Peggy and Chazdesigns T____T) or has eyebrows, makeup, tattoos or piercings.
Beds with low comfort and energy ratings
Hairs that have strange animations, gaps, are not binned, or are binned in the wrong categories
The one thing I hate the most - hairs with strange, unnatural colors, you're downloading and there is just a few color options, one black, one brown, one blond and one red, but the "black" hair is not actually black but has strong PURPLE or BLUE tones, or is GREY when it's supposed to be black because of its ridiculously bright and shiny texture, and the blond hair is not blond but YELLOW, and the red hair is actually RED, ketchup-red, no one has that red hair, WTH make a nice realistic more orange-brown tone instead and at least put the hideous ketchup-color in the custom hair bin!
Hairs that are way too BIG (just check out rosesims donation hair #94)
Bathing suits, underwear and sportswear with high heels
File names like "hair.rar", "hair1.package"
When people place trees in their neighborhoods when they're creating them in SC4!!! The trees look good in SC4 maybe but when you play the neighborhood in TS2 their placement looks AWFUL and it takes like an hour to delete all hideous unwanted trees from the neighborhood just because you HAD TO add them in SC4. Don't.
When people are too lazy to take pictures of their SC4 hoods and you can only see that weird pic in-game and wonder "what the hell is this? What does it look like?"
Meshes with corset-thin waists and deformed feet like the ones from Simchic. I also hate when people use that stupid simchic nude-mesh with high heels for everything they make (you all know which one I'm talking about), especially jeans and pants, so that the clothes fit so tight that they look like they're painted on her skin... Ugh. You can find a lot better meshes.
That's all I can think of :p

-Shiny Skintones
-Bucket Filled Clothes (Yuck, Put detail in them creators)
-Ugly Hair, Non-detailed hair
-Heels on Swimsuits (nobody does that unless they are just "tanning")
-Shoes with Underwear (I had to uninstall one that had that, took me forever to find the file)
-Bed Sheets that look totally un-real (Like a black bucket fill with just a picture of something, make your beds detailed!!!)
-Objects that go through the walls
-Bucket Filled Furnishings. Ew!
-Objects that are the wrong size, And make it go through your sim
-Lipsticks with teeth showing! (I just hate it!)
-Un-realistic Skins
-Pink,Blue,Green Hair! (Its OKAY for techno videos and stuff, But not for like "Passionate love stories"

No more venting for me.
I've gotten all the anger out...
Theres probabally more that I've missed..

the only thing I don't like is low quality textures, false advertising (using photoshop to enhance the preview of the content), and long load times.

JanePstar- I actually look for swimsuits and underwear that have the shoes on version as well. It's better for contests with swimsuit or lingerie shoots.

SC4 neighborhood terrains with trees. Ughughughugh... :eviltongu

Not-binned eyebrows and no grey eyebrows.

- Expensive looking beds with 1-3 points for energy and awesome stoves with 1 point of hunger.. I don't like my Sims to sleep for 10 hours to restore their energy and being hungry.

* Hair that isn't binned correctly.
* Hair that isn't animated.
* Clothing that gets holes in it when your sims are moving around.
* Beds where the bedding doesn't fit it properly or the bed frame disappears into the wall.
* Beds that your sims can't woohoo in.
* Clothes that have really skinny waists that make your sims look anorexic.
* Furniture that your sims sink into or makes some of their body parts disappear.
* Clothing with high heels that make your sims legs look mangled.
* Objects with every low energy, fun, hungry points.

Edit: Oh yeah, there was a bathtube that I downloaded once that made my sim's skin turn green after they used it.

-Objects that are catagorised wrongly.

-Objects that don't have a catalogue description/use the cloned item's description/only have the creator's web address as a description.

-Objects altered in a way which mean the animations don't line up. Even EA is a culprit of this; HEMNES small dresser anyone? The Sims use an invisible handle to open the drawers!

-Clothing that has seams that don't meet.

-Athletic outfits with bare feet. This looks rediculus when they appear as joggers running past your lot in bare feet!

I hate false advertising. I usually don't go for the photoshopped enhanced screenshots anymore. If I can't tell what it's going to look like in my game, it has no use to me. ;-)

I spent last week downloading all sorts of CC for my Sims and remembered why I stopped doing it. I'm also a game artist, so I do this stuff for a living and I can't help myself from picking up on bad work. I'm not going to comment on realistic vs. Maxis-cartoony because that's really just personal taste and I don't really care if someone else likes to make their Sims super realistic or anime looking or whatever. However, I will comment on the quality.

- no attempt to actually have standard hair colours that fit with the rest of the game .. reds and blondes are notorious for this. I don't mind if there are other recolours, but please make base colours that matches the Maxis colours at least as a base! I hate throwing a beard on a red head dude that doesn't match what's actually on his head. That sort of thing.
- non-animated hair (really bugs me! Nothing like seeing long flowing locks that doesn't actually flow but rather sticks up and through the Sims meshes and non-animated pony tails make me cry)
- awful alpha maps that look blurry, chunky or scraggly.
- textures that look like someone just hastily slapped a photograph over it and called it a day with no attempt to make it work with the mesh.
- awful UV mapping... just like the previous point, but also when there's no care in blending where different meshes or textures meet such as the hairline.
- unrealistic body meshes (there were some clothes that I would have liked to have downloaded but the meshes gave Sims little anorexic waistlines and humungous boobs. I know I wasn't going to comment on style, but I find it funny when people go out of their way to make realistic Sims but the bodies just look like unrealistic Barbie Dolls)

Um.. that's all for now. :-D

Ahh, I don't have many CC for my game..
I never knew that there are skintones with eyebrows provided...
I hate shiny/wet looking skintones, open-mouth lipsticks & unanimated hair.
o___o

Oh thisthisthis. I've been through so many terrains that I gave up on because of the trees. My laptop can't handle it and I'm too lazy to delete it all.

I also hate hair that isn't animated, shiny/wet-looking skintones, open mouthed lipsticks, and clothes with patterns which look like they're embossed or digging into my Sims skin.

I have another one!
I downloaded a bench yesterday that looks like it should seat two Sims but only has a one tile footprint and shows in the dining chair section!

anime hair drives me around the bend, as well- I feel like screaming when I google 'sims 2 male hair' and stuff like that comes up. I also get annoyed at clothing without fatmorphs, classing an outfit with heels as athletics wear and badly made shoes, and tasteless/ completely OTT clothes.

however I am guilty of falling in love with the 'shabby chic' grunge- type houses over at places like GOS, even though I couldn't live up to my knees in old records and stained furniture in real life...

-Wrongly categorised clothing and other items.

-Custom Content that doesn't actually show up as custom content, and gets into all your Any Games.

-Athletic Wear without shoes or with heels.

-Hair that isn't animated.

-Hair that doesn't match up. Same with clothing.

-Rainbow crazy maxis match hair and recolours! Hor-ri-ble!

I hate ultra shiny skintones, and also ultra matte ones. I'm a huge fan of realistic eyes and cannot stand the anime-cartoony style eyes. Also, I hate hair that looks great on the pic shown when you download it but then in the game it's not animated and has gaps and sharp lines everywhere...

Oooh, new pet peeve, speaking of shiny...

Shiny hair! I mean, artists that paint the "shine" on hair textures. Please don't do that. It looks awful in most ingame lighting. You can get away with some highlights or what not, but attempts to make hair look shellaced and reflective just doesn't work. This is why people are complaining that some "black hair" downloads look grey. I'm convinced people who paint the hair shine have crappy graphics.

Any body meshes with poorly-meshed high heels (usually too thin/high)
Any body meshes with waists that are too narrow or hips that are too wide
Any otherwise good-quality clothing that looks "plastered on" with no regard to layering, etc.
Any poor quality textures, especially on clothing
Hair meshes with gaps
Stiff hair meshes
Unrealistic shades of red hair
Expensive beds with 2 Energy
Clothes w/o a pregnant morph

* I can't stand incorrectly binned hair and/or clothing
* Anime hair
* Super shiny hair
* Gaps in hair
* Skins with eyebrows
* Lack of thumbnails for accessories that you can't see on the sim preview face
(such as; nails, braclets, rings)
* Clothing without fat/preg morph! grrr

• Screenshots that've been photoshopped so much it's hard to tell what kind of quality the actual download is. It tells me the creator knows there's something wrong, but doesn't care to fix it. I -really- hate it on hairs because it's not always easy to tell that they've just covered the gaps.

• Items that don't fit the grid properly. Like where they only need one square to be placed, but the item itself is sitting on three or four? That kills me.

• Clothes that cinch a sim's waist. It's just so creepy to me for some reason.

• Food that isn't animated.

• Paysites.

• Young clothes for elder sims. Bleh.

I agree!! I don't mind some more youthful and fresh looking outfits - not every grandma in my game needs to wear dowdy long dresses - but you have to draw a line! If your cute saucy Sim in college would wear it, grandma shouldn't!

Hair where the "default" shades really belong in the custom bin, ie: red is fire-engine red, blonde is yellow etc. Blah!

houses with plants that are impossible to get to so they die, but when you get rid of the ones that died, you have to get rid of nearly ALL of them or it looks vacant and stupid.

i can't complain about much though, because i can't do anything myself.

My only major pet peeve in cc is when I download a lot, and they didn't include enough space to the side for a driveway, so I have to tear down some walls, and then do all the work they didn't do and build my own driveway.

Finding something I just love, only to find out that it's a recolor and the link to the mesh leads to a paysite! I totally hate that!

When you try out a downloaded custom object on the sims and the animations are retarded and make your sim look really strange.

Really pixellated clothes and hairstyles.

Custom objects with stupid names.

Everything else has already been mentioned.

But, There is so much custom content that is actually really awesome! Especially on MTS!

I hate cc...

1.Clothes with no fat or prego morph.
2.Clothes shown in all catagories.
3.Clothes that are poorly photoskined or they just dumped a bucket of paint in it.
4.Clothes that are blurry or have no detail.
5.Clothes with very poor alphas that they do not meet up at the edges correctly.
6.Low poly.
7.hair gaps
8.maxis like skintones...(I like realistic skintones.)
9.most skintones with brows...(unless it is a celebrity skin.)
10.cc files without a good descriptive name...stuff like fg893kl7...wtf?
11.not enough elder cc.
12.uploaded lots that require all ep's...it just sucks! Why can't there be more BG lots.
13.TSR...most of it is crap.
14.PAYSITES & Asian sites that do not freely share thier cc.