Something that really annoys me, and will get your character refused from my RPs, is characters that go against the setting of the RP. If I have a roleplay set in ancient China, you can't use katanas, because they're Japanese and it would have literally been impossible for you to get one! Or if I have a high fantasy setting and somebody makes an anime ass dog girl. Having characters with animal qualities is fine, but not when the are straight out of an anime.

You can do plenty of things with your characters and still keep it to the setting. Really, it's not that tough to do some research and see if the weapon, name, or whatever you chose fits the setting the GM has set. Or, just ask, so I don't have to refuse your character.

Another thing that comes off of that is people who get pissy when I refuse their character for not fitting the setting, or ignore the suggestions I make to keep things in the setting. If they want a katana in a Chinese roleplay, I'll suggest to them a Chinese sword that's similar to the katana.

Basically, I hate people who try to join a roleplay when they obviously know nothing about the setting surrounding it.