when she came back to serve, singing a song with her name in it (I think the girl's name was Mary and she played for SMC - this was maybe two years ago). They got the girl to actually give a smile. It was both funny and sweet at the same time.
Such obnoxious students!
But normally I assume they are just telling the server that he/she will choke, or serve the ball out or something. Someone else will have to give the details.