Originally Posted by Stokke
He recently met an opponent who yelled YES! YES! regulary when my son double faulted or when he made an unforced error.
Laugh out loud when the other player does this. Relieves your own tension, and lets him know that you think he is a buffoon, while not actually saying anything that would get you in trouble with an official. Most people really don't like being laughed at, especially when they suspect that they deserve it.