This is going to sound kinda of fanboyish, but:
I found throwing a knife into Shepherd's eye socket at the end of MW2 intensely satisfying if only because he had no reason to shoot Roach and Ghost in the first place. I have played the damn game twice and I still can't figure out why he needed to kill us to get the data, when we were giving it to him anyway. I mean, we were working for him the whole time, we hadn't even seen the data what made him so sure we needed to be killed, for no reason?