Disaster Button said:
Oh this is easy.
"Astalavista, baby"
-The Terminator.
When I heard this so many times, I thought of it as cliche. But then I saw the movie, learned where he heard the first phrase, and thought of it as an awesome throwback after that.
There are some good ones from TF2 though;
Soldier: If god had wanted you to live, he would not have created ME!
Heavy: I AM GOING TO KILL YOU AND KILL YOU AND KILL YOU!
Scout: I will never stop killing you!
Demoman: I'm a grim bloody fable with an unhappy bloody end!
Demoman: (vs pyro) Go to hell and tell the devil I'm comin' for him next!
Spy: Right behind you.
Spy: Oh, soldier, who will they ever find to replace you? ANYONE! Hahahaha!
Medic: Would you like a second opinion? You are also ugly!