Argumentum ad hominem,

Is not necessarily a fallacy, although it often is. Sometimes who the man is is extremely relevant to a discussion—or in fact ending a discussion. 
At least this "fallacy" is often abused.
It's often complained "hey, that's ad hominem"—and yes, it is, but it doesn't mean it's a fallacy. It's against the man, but in this case the man is someone shitting up tha birthday party.