I have two suggestions 1) report 2) refuse

tell an adult. don't be an asshole back to him. don't hit him. TELL AN ADULT. adults are cool and powerful and can do cool shit like punish the bully or change buses for you.

i know force your mom to swich bus's m8

Tell him he is a jerk and he needs to rethink his life

Give him bland responses like " ok " or " whatever " , but, if it's PHYSICAL get an adult or teacher