Here are a few we use:
Tim again- My brother Tim always seems to want to take another shot, if he didn't like the first shot, so when ever we need to take a mulligan, we say, "I am going to take a Timagain".
Dirty Putt- A putt that hits the basket and looks like there is no way it should have stuck, but some how ends up in the chains.
Get new- We holler this when a disc starts to get understable, and we want it to come back, since most new discs tend to be a little overstable.
Buck shot- when a disc leaves you hand and goes off in a direction that you didn't intend it to go.
Worm Burner- A throw that leaves your hand and goes straight down and skids along the ground.