Similar to the Jizz Grenade. While recieving a blumpkin, you shit in a big balloon rather than using the toilet. Then have 6-9 of your friends masturbate to you and your partner and then when cumming, jizz into the balloon. Once the blumpkin reciever is cumming, he then jizzes into the ballon. They then throw it at a victim yelling BOMBS AWAY!!. This makes a prank that a victim will never forget for many many years.
Alan: Man, Mitch is such a fucking dick.
Nick: Hey tomorrow lets build a blumpkin grenade so we can teach that bastard a lesson!