It's a tough question. All I can say (for what it's worth) is, I can not make myself applaud a bad performance. To encourage someone who is obviously tone deaf and doesn't know it, or worse yet, does know it and still wants to torture an audience is beyond me.

Seems to me that the obvious solution is to simply leave when the no talent "singer" starts. If we all did that, they might get the hint.
Personally, someone singing or playing off key is painful to my ears and I just can't tolerate it.

That's a personal opinion. If I had control over it I would just ignore it until it was finished, but, it makes more sense to just leave.