McSummersault Share definition Flag Diarrhea so incredibly intense that you do a backflip/frontflip/barrel roll off of the shitseat. Yesterday I got a quick burger after work, and that night I did a McSummersault. IT WAS EVERYWHERE!!!! McSummersault by Flypigzen December 5, 2009 0 0 Get merch Get the McSummersault mug. Buy Now — $32.95 See more merch