When a girl that has a flabby ass uses tight jeans to hold the ass in place. You can still tell as it is trashy. Like a garbage bag overflowing, if the jeans ever exploded, you would have a mess. Abbreviated as GBA
Matt: Jeff do you think my ex-girlfriend is hot?
Jeff: Not really.
Matt: Why the f**k not?
Jeff: She has a major case of garbage bag ass.