in the military we call this a barracks lawyer. someone that has it almost right but gives advice that will get you in trouble.
rolling up next to someone and revving on them to race is not entrapment if the person takes the bait.
entrapment is defined as when the police coerce someone into doing something illegal that they would not have otherwise done without the coercion.
if the cop acts like the average sat night street racer and trys to entice someone into a race by a little red light revving or something to that effect its not the cops fault if the person hammers the throttle on the green.
now if the cop offers the guy an enormous payout of the person wins the race or something like that then entrapment could be argued.
this is from the california lawbooks but the definition still applies
Entrapment
this is what you do if an umarked lights you up
http://www.co.ho.md.us/police/docs/tipsonunmarkedcars.pdf
its obvious i am a cop isnt it.