When someone throws fast food bags out the window of their car because it is filled with them and they are too lazy to find a trash can.
Dude 1: "Dude I found a whole bunch of fast food bags in the bushes outside my house..."
Dude 2: "Oh yeah, that was me... every time I come over I eat some Cajuns and dump the bag in those bushes."
Dude 1: "You lazy ass! Can't believe you would do a fast food bag dump off by my house!"
A dump resembling when a grocery bag is overfilled and the bag rips, immediately dumping all of its contents at once. Grocery bag dumps usually occur after large meals and waiting until the last minute to defecate.
I'm glad I made it to the bathroom in time. I had to take a massive grocery bag dump. I feel much betternow.