Needs a Better Description
When a character, either feigning genuine laughter or being obviously sarcastic, pretends to laugh along with other characters, or encourages/threatens them to do so, then abruptly tells them to shut up, in one way or another.
Examples: In Toy Story
, when Bruce the shark finds Woody's hat and does a lame impression of him, Woody does a version of this.
In Labyrinth, Jareth pulls this on his goblin Mooks after telling them the "you remind me of the babe" joke.