When someone with intestinal issues (e.g. diarrhea)attempts to fart and up until the last instant doesn't know whether it will be a shart or a fart, in effect gambling on the outcome. Different than a shart, however, the results of losing the Bet on the Gambler can be significantly more catostriphic.
The large stain in Lucy's pants made it clear she Bet on the Gambler and lost.
by RMDB September 23, 2008