I did a set at a bluegrass festival for a friend. He asked me to sing a particular song about a dog.
There was a nit wit walking back and forth in front of the audience saying, "I can spell dog, "DOG"..I can also spell cat, "CAT". then he realized that I was giving him "the look". he looked up at me with a sheepish smirk on his puss, and when I said to him, "It's ok, keep going, I can't wait 'til you get to chrysanthemum." he headed for the exit to a great clapping. He never came back.

In Scotland, a couple of the audience asked if they might be permitted to heckle me. Never had that before, or after. One did ask a funny question.

An old friend of mine had a daughter who didn't take prisoners. She worked in this joint, and some pie eyed sot said to her, "I'd like to get into your pants." She replied, "What for, there is already one ass hole in them."

I tell this one in the first person because it scans better.
I was served by a beautiful waitress, and I asked her, "Where were you when I was single and available"? She said, "I wasn't born yet."