Pet peeves:
"On the hold." No such animal, ICAO or in the AIM. This phrase was the first step in a near miss in DEN several years ago when it was confused with "On the roll." It's "Position and hold" or "Line up and wait" if flying in some overseas locations.
Dropping part of your call sign before ATC drops it. I don't know how many times I have heard this exchange- ATC: "______ 1234 Sierra Pappa, cleared _______." Aircraft: "Sugar Pappa." ATC: "Okay- which Sierra Pappa just responded to me?" I hear this with airliners and military as well, so not just a slam on GA.