Heero Yuy from GundamW: Although he probably gets less evil, Heero is one of the only hero I know that laughts like a maniac each time he kills someone. And he actually treatens someone with a gun because "she knows too much". Definitively evil!
Sagara Sanosuke from Rurouni Kenshin: He's a born fighter which would pick up a fight for no reasons. He also leaves th restaurant without paying and lives freely without working.
Tira Misu from Bakuretsu Hauters: Treating the person you love like that just because he's chasing another girl or because he turned into a big monster, you have to be evil.
Tasuki from Fushigi Yuugi: He burns poeple on purpose, and not just bad guys. He is also the leader of a thief gang.
Takeshi (Brock) from Pokemon: With those eyes always closed, you never know where he's looking or what he's thinking! (Although he's probably blind, dressing like that.) Plus, he might be a Mazoku.
Takashi from Video Girl Ai: Wearing your hair like that, you have to have some kind of relationship with the devil. Plus, his little plans to help Youta are all kinda evil.
Mikagami from Recca no Honou: Okay, he's not really evil, but we could use a guy like him on our side.