\I would be tempted to use joel givens' heckler stopper, from session, but i think i would refrain. i used to use it alot, in the past, but i've matured a little (very little). Ask them what the problem is. nine times out of ten, they'll say they don't like magic, or it's boring, or they know what you're doing... In which case, i simply say 'well, y'know, if you think you're wasting your time taking part in this, you can always leave?'
This works 90% of the time. You have asked them in a calm manner what the issue is, then gave them a suggestion on how to deal with it. they don't really have anywhere to go from there! If the spectator is drunk, they will be erratic. it's in these situations that i would use my own heckler stopper- a deck vanish- and ask 'well, now nobody gets to see anything, because you're so cool'. in this case, i don't have to do anything, the other spectator's will do it for me.
In a professional setting such as a restaurant, i would simply take what they had to say, and move to the next table. You cannot argue with the customers in a restaurant!
Chr!s