I've seen funny names in-game without a forum account.
- HornyJew
- Some_Nigga
- NotLeafyGreenTea
But when you say "best usernames" do you mean the best players you've ever talked to/seen in game?
I've talked to NoahSailer before he was Number 1
Graveyard I've talked to in-game
Me and Edtheg used to be friends (kind of still are)
Reven and I have teamed before once or twice
Philly67 and I used to be friends
Zietra and I are friends
CharlesYummyEgg I've teamed before and did FFA's with him in games before
E.T.C.