Some more:
Red mist: As stated above - anger towards another driver that makes you drive beyond your ability.
Shunt: smacking a wall with your car.
Push / Plow / The car's tight: Understeer
Loose / fishtail : Oversteer
Too hot: too fast
Bench racing: discussing what an awesome driver you are AFTER the race / event is over.
Bus stop: A Chicane built into the track in order to slow down the pace at that section of the track. (aka "The Inner Loop" at Watkins Glen)
Keep the shiny side up: be safe, don't flip your car
Keep it between the grass: stay on the asphalt, don't fly off the track
Collect: hit another car. For example: the guy spun out and stopped in the middle of the track just waiting for someone to collect him.
PEBSAS issue: A bad driver. (Problem Exsists Between Seat and Steering wheel)
Momentum car: a low hp car.
Invisible flag: aka the blue (you are about to be passed) flag
Meatball flag: (Black flag with Red dot in the middle): Mechanical problem with your car.
White Knuckle grip: (aka Death Grip): holding on to the steering wheel with 142lbs of force per finger.
Late Apex: when the car is nearest the inside of a turn later on in the turn.
Early apex: when the car is nearest the inside of a turn earlier on in the turn.
As you know, a blue flag means someone's about to pass you. A white flag means there's a slow moving vehicle on the track. Therefore, a combined BLUE and WHITE flag means a 914 is about to pass you!
I know some of these aren't slang, but you may be able to work them in!
-Z-man.