A. Ignore them. I've held up a "wait a minute" finger and most will either wait or return to their seat.

If they don't take the hint use the next finger down the hand turning the palm of the hand towards yourself.... perhaps they will take THAT hint.

Or.... you can always STOP the song and the show.... explain to the audience that THIS buffoon thinks he or she is SO important that they will not wait until the song is over like everyone else to make a request..... embarrass the idiot.... of course, if they're plastered, the hint won't work nor will the non-verbal communications, and very likely they are beyond being able to be embarrassed either.

If this problem persists, get a note pad for idiots like that to write the request on a piece of paper..... we used to tell the audience, multiple times throughout the evening's show.... "If you have a request, please write it down on the back of a $20 bill, wrap a quarter in it and toss it up here.... if we don't know the song, we'll be glad to give you your quarter back". Some folks actually did that.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.