report that plate number for aggressive driving and possible intoxication by phone right after it happens. there's no reason someone who's sober should behave like that, and his erradic driving is only more proof that he must've had a few drinks. I'm not sure if that would cause him any more trouble, but its worth a try. Or just go to a payphone and phone in an anonymous tip that you saw him selling drugs to little babies right after he knocked off a hooker, peed in a cop's gas tank, spilt oil in the gowanus canal (not that anyone would really care about that), made a comment about taking down the goverment "by any means neccessary", spit in some donut batter and clubbed a few baby seals.