I think Custer's Revenge really takes the cake here, but since I've never personally played it, my vote goes to Tag Team Wrestling on the NES.
The player controls the "Ricky Fighters" and the computer controls the "Strong Bads" (yes, fans, this game inspired Homestarrunner...you can see a copy of it flying past when Homestar seeks a present for Strong Bad in one episode). You basically fight the same match over and over and over again until you get tired of it.
The game has about two songs and the characters often seem to skip multiple frames of animation. In one frame a guy is running, and in the next he's in mid-air kicking his opponent. The terrible animation combined with bad hit detection makes it pretty difficult to tell when your attacks will actually have any effect. The computer players also randomly get "mad" and become invincible until such a time as they hit your character.
The game is actually good for some cheap laughs with it's terrible Engrish and crazy gameplay, but wow, bad.