look up any word, like b4nny:
 
2.
Having sex in a casual or non committal way.
Dude, me and Robyn did the Rumper Bumper last night!
by mregina October 14, 2008
 
1.
The rear end of a shapely woman.
She fell on her rumper bumper and suffered no damage.
by Brian Babylon September 03, 2011