Some of the wretched low-budget slasher movies I've seen have to qualify. Can't remember all their names, but a few that stick out as awful are the first Sleepaway Camp movie and Silent Night, Deadly Night 2 (the first half of this film literally consists of flashbacks to the first movie - what a cop-out). I should also mention Bloody Murder - a plot that starts off as literally a Friday the 13th knock-off even down to the killer in an ice-hockey mask, then tries to be a send-up (maybe out of desperation) but hasn't the knowing humour to make it work. Then there's some of the monster movies I've seen. The older ones with dodgy-looking monsters that turned out rubbish were at least so bad they were kind of fun, but now the better monster movies out there are drowning in a sea of films with bland CGI and non-existent storylines (think the Sharknado films, Mega Shark Vs Giant Octopus, Jurassic Shark for 90 minutes of total tedium). I might also mention The Phantom Menace and Godzilla '98 (there are two franchises I'm amazed recovered from those depths).