I get this all the time.. I usually do this if a person asks, I tell them "I would let you on, and you probably would do a great job, but I've had like 15 others ask me, and they sound terrible! And if I let you, have to let some of them sing to, and neither you nor the crowds wants that, trust me!"
If this doesn't work, I let the guy do one number, which is usually terrible. When the crowd think is karaoke time, the next one who asks me I say: "I would, but did you hear that other guy?? man that was awful, we can't have more of those, and if you get up and sing, we most definatly will have more of him, and you don't want that do you?"
This usually works.
Doc-Z
[This message has been edited by doc-z (edited 11-29-2006).]