Pedro W. Mendez?
-Mmmm... no. Not the worst... He's actually pretty polite to those he respects.
Although when it comes to openly cussing at other characters, this guy wins.

Oh... right... Alexandria Sheppard. My spy-character...
-Brutal bathroom-stall murder followed by stealing the victim's face.
+To be fair, she was trying to escape from contractual slavery at the time.

--I've also had an alien dismember and eat his human-girlfriend's father. But again, to be fair, her father was a crotchety dick with a shotgun.

Non-character based things:
1. Overthrew a nation by capturing their nuclear warheads and detonating them on their own soil, then brought their leader's head back on a stick. To be fair, the guy had it coming. 
[u]We call it plan magenta.[/u]

2. Started a revolution by kidnapping a sapient weapon-platform that happened to look like a little girl.
-Also, brainwashed the weapon to fight for our team.

3. Started a few [total thermonuclear] wars via forged diplomatic communications.

4. RPed a guy getting steamrolled under some tank-treads in a fallout-RP.
-In same RP my character also straight-up murdered a peeping-tom shortly before serving 'milkshakes' and 'cheeseburgers' to a lactose-intolerant woman.