When I was just starting off, we had a for fun tournament in a local city. A guy we were watching kept yelling "COME ON," but the way he said it made it sound like "HAM BONE." From then on, all the guys on our tennis team would yell "HAM BONE" to each other for encouragement.
Our high school team had all kinds of quirky sayings, just little things we found funny, like turning to a partner in doubles and saying "Sack lunch!" and making eating motions/sounds after an overhead bounced over a fence, things like that. I'm sure other people thought we were weird as heck