1. The Joker
Come on, guys. The Dark Knight came out years ago. Heath Ledger was amazing and it makes sense that awkward misfits would want to emulate the character. But you're not Heath Ledger. I know you want to prove that you're dangerous and clever, but spraying your hair green and running around a convention center asking people if they wanna know how you got those scars is not the way to do it. Gotham deserves a better class of cosplayer.
This guy is allowed to cosplay The Joker. Everyone else should stop.
2. Harley Quinn
The Joker's girlfriend doesn't get a pass, either. Look, Harley Quinn is fun, I get it. You can be sexy and dangerous and silly all at the same time. Which would be great if 500 other women didn't have the same idea. Everywhere you look you can see red and black costumes in varying stages of undress. It's impossible to walk the floor without getting whacked by at least 20 giant papier-mâché mallets. At that point, it stops being clever.
Nothing says "don't fuck with me" like foot-long steel claws and mutton chops. Wolverine is a favorite of dudes who want to look cool. Who are you kidding, though? You're at a comic book convention, it's impossible to look cool. It looks like you're trying too hard, which is the exact opposite of cool. When you get right down to it, dressing as Wolverine is just an excuse to walk around flashing your guns. And unless you actually have the arms of Hugh Jackman, we don't want to see it.
I know what you're thinking. "This movie only came out a few years ago! There's no way it's overdone, because we haven't had time yet!" You're so wrong. I can guarantee you that no matter how beautiful your costume is and how much you identify with the character, you won't be feeling as excited when you're standing in line with 17 other Elsas to buy 5 dollar water. It's not a good choice. Just let it go.
5. Any Incarnation of The Doctor
I know cosplaying as The Doctor seems like a great idea. It's both easy to put together and easily identifiable which makes it ideal for guys who want maximum recognition with minimum effort. You'll probably feel like a rock star. Little kids will want to take pictures with you and maybe a pretty Rose Tyler will want to play with your sonic screwdriver. The thing is, all the other awkward dorks around you wanted to get in on the action too. Time Lords only get 12 regenerations, so 400 Doctors wandering around makes less sense than Steven Moffat's writing.
6. Slave Leia
Come on, ladies. This costume was intentionally degrading. Jabba was trying to humiliate and sexualize Leia because she was enslaved. It's not fun, it's not empowering. It is, by its very nature, objectifying. Don't put yourself through the chafing and ogling just to prove how enlightened you are. Unless you think you'll need to choke out a giant mafia slug. In that case, carry on.
7. Steampunk anything
Steampunks are the hipsters of the cosplay world. They try to make everything look vaguely used and are super into weird technology. At first it was kinda cool just because it was different, but it's gotten old real fast. What's the point? To make it look like Iron Man was some kind of mechanical Frankenstein? What other Victorian stylizations are you adopting? Did you shower in the last month? Do you think hysteria is a thing? All of these are questions you'll have to answer if I see you wearing anything steampunky so it's probably best to just leave the weird goggles at home. (Seriously, what's with the goggles?)
8. Zombie anything
This is another one I just do not understand. It doesn't make sense to zombify your character just because you took a stage makeup class and you really wanna break out that liquid latex. Unless the character is actually a zombie, or there's a legitimate reason to believe they might be, leave it alone. If all you wanna do is make a gross wound, do it and just tell people you're from The Walking Dead.
You know what, guys? I'm being a pretentious asshat. Do what you wanna do. Except, please don't wear a metal bikini. I'll always think that's gross.