Playing a Predator in AvP 2010 is ever so satisfying if you're in a bad mood or someone just made it into your bad books...just find a human, pretend it's them, and rip their head and spine out through the hole in their stomach that you just fashioned with a wrist blade. VERY satisfying.
I also have this thing going for me with MW2 when I hop onto that online, where if I'm in particularly bad form, and am getting absolutly demolished (and pissed off), I will say to myself "Ok, if I die three more times in a row without getting a kill I'm ragequitting..." and about 9/10 times I will get a kill before then. Sometimes this works and makes me do much better out of determination and self imposed ultimatum, but other times I'll actually be annoyed that I got a kill because it means I'd have to stay longer in the match.
I have a rock solid sense of determination and self disipline.