This is so obvious. "I kill him!" "No, you wouldn't do that." "I, uh, I just said I did?" "No, you don't. You didn't start. You wouldn't do that."
Except when it's not obvious, right? "Wait a minute ... I was about to said 'I kill him' about ten times during that scene, and somehow I never got a chance. Or when I did, you treated it like my character was just thinking about it, not starting to do it."
Control of a player-character's decisions, or opportunities for decisions, by another person (not the player of the character) in any way which breaks the Social Contract for that group, in the eyes of the character's player. The term describes an interpretation of a social and creative outcome rather than any specific Technique, but subtly or unsubtly entails the use of Force. Commonly responded to with various forms of My Guy tactics.