Welcome to the reality of bicycle riding. Teenagers with nothing else to do, showing off their bravado. I'd try to make a mental note of license plate and car type, maybe the driver of the vehicle, and if it happens again with the same 'perps' maybe contact the local PD. If no physical harm, just taunting, consider it a 'no foul' situation and let it go.

"Sticks and stones can break my bones, but words will never hurt me."