I know a lot of people do this so I'm worried I might ruffle feathers, but...

People who have a stock selection of characters that they use for all the RPs they play in. If I'm GMing an RP, I want people to come up with characters to fit the RP, not crowbar their old ones into the setting.

To me, this practise doesn't say "I really like this RP's concept and want to embrace and be a part of the world" so much as "I really like this thing I've already worked on and now I get to use it again", which isn't really very inspiring.

I'm sure plenty of people see it very differently, but that's my reaction to it.