Kane & Lynch: Dead Men

In Fragile Alliance multiplayer, if someone kills you and becomes a traitor, if you kill that person when you respawn that is personal revenge. Do this three times in the same session and this achievement should unlock.

Play a 3 round session.

Hold your grenade, and have another player kill you and then stand on your corpse or look for where the primed grenade rolled (can't be far from your corpse) when you died.

Do this for 3 rounds and the achievement unlocks.

You can easily boost this with a friend. Host a game of at least 3 rounds and when it starts stand close to your friend, drop a grenade at his feet, have him kill you before it goes off (after you die your grenade will kill your friend and count as a personal revenge). Once you respawn as security finish the round quick then rinse and repeat. Make sure that your friend is NOT a traitor before you drop the grenade otherwise your kill will only count as a regular traitor kill.