Oh I've seen this joke before, slightly better, but now I don't know which was the original.
It was like
Bard: I cast vicious mockery
Dm: cool. What do you say to him?
Bard: "You're none of your best friends' best friend"
Dm: ...
Other players: ...
Bard: So do I roll damage or...?
Dm: No... No, he's dead.