Thing ruiner
Quite simply, a person who ruins a thing. May be a person who kills a joke, or simply is just an overall buzzkill. When someone ruins a thing in a group of friends, it is the responsibility of the rest of the group to point and shout "thing ruiner,' to let him or her know of his or her error.
Me and my bros were listing the greatest rappers of all time, and my friend yelled out OJ da Juice man.. We had no choice to all simultaneously yell out "thing ruiner"