Quite obviously, it has to be Dangerous Streets.
I agree 110%. Without a doubt - Dangerous Streets - the worst Amiga game, ever. I think the bundling of this game in the A1200 magic pack was what finally killed Commodore. ;-)
Other stinkers I seem to remember include Days of Thunder (though the C64 version was even worse!), Several of the Brutal Sports titles, and Nigel Mansell's Grand Prix. Even Psygnosis had a few.... Air Support, anyone? Maybe Combat Air Patrol, as well. CAP suckered me into an ill-advised purchase. Amazing demo -- it was fast, beautiful, and playable. Three things they managed to remove for the full version.