so many...all the elder scrolls games, a game called "dungeons, the dark lord", or a game called chivalry Medieval warfare and you could pick the masons side, and i'm pretty sure like 80% of all rpgs, or you could play multiplayer games and betray your team mates, which is truly evil! and thousands more than my brain can call up at the moment...there are many many to choose from, my fellow minion of evil. I for one just give my character an evil background story in any game i play, and make all the worst choices. It always makes me feel...like this--->
http://www.youtube.com/watch?v=ODRoEHpUdrU

APB reloaded a f2p shooter action game you can play as a criminal.

The Fable games.

all good choices

Evil Genius

Dungeon Keeper. Enclave too (two storyline branches, one good and one evil). Not strictly bad but relatively open to this idea are god games like Populous and Black & White. People say that Star Wars: Knights of the Old Republic has some well executed evil aspects too, though I'm always sceptical about RPGs. Going evil in those often results in the numbers of quests and things to do getting minimized simply because your evil actions would often kill quest givers, or so at least it feels to me.

You play robbers/heisters in Payday.

All the GTA and Saints Row games.

Just buy any game with multiplayer and be a Di.ck

The Fallout games.

Zombie Panic Source - you can be the zombie team right away by pressing F2 at the start.

why is it playing as a "bad guy"?

should be fun guy play style