Is One_Burnt_Potato amusing?
Haha, I was gonna post yours actually as I remember playing you - t'was a funny username to be honest.
Anyway, these are some that I liked (and the only ones I can think of off the top of my head, heh):
FOCK_THAT - Made me laugh because everytime I killed him / her, I could go, "Fock that? FOCK YOOOOU!"
God_He's_Good (or something like that)
Also, people tend to like one of the guys I'm always partied up with's username which is IbuyPIEguy.
buttwolf is one of the funnier ones I've run into.
Rofl, you ran into him too? My party encountered him once and pretty much never stopped saying that name for the entire match.
He ended up ragequitting.
Most of these sexual innuendo screen names are quite lame and are juvenile names someone in junior high created, but I do find amusing:
LoadInYourFace or reLoadinYourface