Jokebombing

To interrupt a joke someone is telling to someone else by jumping in and yelling out the punchline.

Dave: Hey Joe, what does a black man do when he laughs?
Joe: lol i unno dave, what does he do?
Dave: He -
*Michael appears*
Michael: HE SNIGGERS!
Dave: Shut the fuck up Michael, you jokebombing little sniggerer.