brake test
Speeding in front of another driver and then immediately applying the brake, causing this driver to have to stop quickly as well - testing the brakes on their car while evening the score.  Usually used as a retaliatory measure against a stupid driver who has pissed you off.  Works well on hypermilers.
As a side note - Brake testing should under no circumstances be performed while your wife/girlfriend is in the car.  They don't appreciate the need for immediate retribution.
"Kevin brake tested the fuck out of that guy!"

Kevin said "I'm gonna brake test the fuck out of this guy - hang on!"