1) Something, especially something musical, that is incredibly, almost unbelivably horrible and is to be avoided at all costs.
2) Anything that causes the same gag reflex as the third repeat of "Margaritaville" or "Cheeseburger in Paradise" sung out of key by balding middle-aged men in Hawaiian shirts and fish-shaped hats. (yes, that bad)
Person 1 - Dude, don't go in there, the singer they hired is Jimmy-Buffet-tribute-band-bad.
Person 2 - But it's my brother's wedding!... Wait, did you say 'Jimmy-Buffet-tribute-band-bad'?
Person 1 - Yup.
Person 2 - On second thought... I'll stay here... he probably won't miss me much. I mean c'mon, I showed up for his first, second, and third weddings.
Person 1 - Smart move.
Girl 1 - Did you see her outfit?!!!
Girl 2 - Omigod, yeah. It was totally Jimmy-Buffet-tribute-band-bad.
Girl 2 - I know! I threw up in my mouth a little when she walked by.