1. The rapid flashing of your cars headlights to tell someone to move out of the way.
2. can be used on slow drivers.
3. From the term "F.U Flash", meaning "Fuck you Flash"
Driver: This bitch in his Mercury ain't gettin out the way.
Passenger: So bring on the Foo-Flash!
Driver: Next time don't drive at 40km/h on the freeway!