my fav:

PASS ME. MAKE YOUR DAY.

GET THE f@CK OFF MY ASS!!  (yes i really saw one like that)

0-60 IN 10 MINUTES

TOO SLOW, TOO BAD.

YOU THINK THIS IS SLOW? KEEP RIDING MY ASS AND I'LL SHOW YOU SLOW!!!

WARNING: I BRAKE FOR TAILGATERS

KEEP BACK OR I WILL FLICK A BOOGER ON YOUR WINDSHIELD

CAUTION: LOOSE PARTS MAY FALL OFF VEHICLE