The act of cumming to aggressive to the point where you lose all control over your body, fall to the ground and bounce like a balloon. The results leave injuries similar to bieng assaulted, hence the 'bashing'.
Man after no nut November my Friday nights turned into a full on Balloon Bashing festival
The act of putting a ballon between your penis and attempting to burst it by thrusting into it onto a partners ass.
“ hey babe let’s start Ballon Bashing that ass”
“I was Balloon Bashing the shit outta my girlfriend last night”