When a woman has an absolutely massive ass, but her ass reeks of fish.
Example girl 1: Walks by, as her butt wobbles uncontrollably.
Example Dude 1: Damn, look at that booty bro!
Example Dude 2: Nah you don’t want none of that Fat Fishy Ass.
Example Dude 1: (holding nose) I think I smell it now. Girl get outta here with that Fat Fishy Ass!!!