In my group, usually the kill 'em all race is usually undead. I don't know why, I think that people like to experiment with the creepy factor (or try to).

I think I remember one game that was probably set up as a kill 'em all game. However, the party (IIRC) consisted of a tiefling, a goliath, a shifter, a half-orc and a dragonborn. And the dragonborn was a (somewhat) reformed evil warlord. In that case, I suggested diplomacy because it didn't really make sense to kill everyone on the basis of race or even past deeds.