An onomatopoetic phrase stated out loud when one has a boner.
Typically, the second 'bump' is stated with higher inflection, and
the volume of the phrase is
representative on how raging the boner is.
The phrase can also be used in general situations of extreme
happiness.
After seeing a tall
blonde girl with huge tits walk past you while
sitting on the park bench with a couple of buddies: "bump bump"
"Hey bro, I just saw that hot ging at that party, and I totally bump bumped."
"
Tiger Woods just won the tournament, our douchebag varsity golf roommate Patrick probably just bump bumped."