[quote=@TJByrum]
I've never been the bad guy in a RP until recently, and I must say I am enjoying it.

My character has, thus far, conspired to use dynamite to block off the exit (so the allies cannot escape), poisoned the food they will soon feast on to demoralize/fatigue their troops, and made dozens of backdeals that - when the time comes - will demolish the player-alliances.  And no one knows it's me.

Life is good.
[/quote]
Easiest way is to rationalize their actions until their morality goes off the deep-end, then keep going into super-villain territory.

Such has resulted in characters that will sit idly by to listen to the hero's sob-story origin, then proceed to beat their skull into a urinal.

This sometimes results in a mind-screw when you discover that despite your best efforts, your villain is the most heroic and identifiable character in the RP. (which is like calling the Joker a hero for the same reasons as Red Hood)
-Example: if an alliance is so flim-flam, that a single person making a few back-deals can tear it apart, is really just a huge lie to keep people calm. Best to break the illusion before it's too late.