This consists of a top shelf (defecating in the water tank of a toilet) performed by someone who is suffering from the symptoms of Crohn's Disease. This condition is marked by peristent loose and watery stools which may include blood. This causes a particularly unpleasant and messy surprise for the next person to flush.
Dude last week me and Eric and Damon were at a bar in Halifax and the fucktard bouncer tried to kick those two out 'cause the three of us were asking girls for blumpkins. Luckily they missed me and I went to the can to give 'em a Crohn's Top Shelf for their trouble. My Crohn's was particularly bad that day so I left them a bloody diarhea stew in the tank.