twenty dogs for the ages - there are definitely even worse movies, but these are some of the very worst that I've been unfortunate enough to see and can remember at the moment
Mannequin
Weekend at Bernie's (never saw II)
The Terror of Tiny Town
Bio-Dome
Jaws: The Revenge
Battle for the Planet of the Apes
Popeye
License to Drive
Soul Man
Hard Rain
Killer Clowns From Outer Space
Daredevil
Pumpkinhead
Basic Instinct 2
Hell Comes to Frogtown
Wild Wild West
Howard The Duck
Psycho II
Caddyshack II
Fire Down Below