Most of the renegade interrupts in Mass Effect 2. Spoilers!
“You’re working too hard…” electrocutes a batarian to death
“You talk too much!” shoots a gas pipe below a krogan clanspeaker, then shoots again, incinerating him
Mercenary: “…I’ve got nothing else to say to you-”
RenShep: “-how 'bout ‘goodbye’” Punts him through a skyscraper window to his death (aliens in the future still use fragile glass, apparently).
“I’ve had enough of your disingenuous assertions!” Punches a reporter in the face.
Pretty much all of the interrogation as a renegade. Damn, I love being bad.
Tossing a grenade at a box of cannon balls as the SS closes in on you, then leaving the room just before the explosion. Come back in, and the room is gone.
Doom didn’t have a knife. The no-ammo melee weapon was either bare fists, or a chainsaw. And the bare fists were actually pretty powerful (for the duration of a level), if you got the berserk pack.