Jaws 3
I know, I know. They made a part four. I also know that part four somehow ended up being even worse than part three, which most would imagine as an impossible feat. But Jaws was groundbreaking, and the sequel was not awful (even though it should have been, as Jaws never needed a sequel). But part three, literally, jumps the shark. It jumps the shark into fucking SeaWorld. It makes the worst use of 3D I have ever seen, and the effects, acting, and story are just awful. Beyond awful, really.
Somehow, Jaws ends up in Seaworld. No joke. As you can imagine, chaos and crappy 3D ensues. What can you even say about this movie? It actually sounds HARDER to make a movie about a killer shark un-scary than it does to make it scary. The premise of a great white in itself is terrifying. Yet in this film, they proved it is actually really easy to make a scare-less shark movie. Suck out any tension, add 3D effects that look like someone pasted a shark they cut out of a magazine onto your TV screen, and make it all seem as implausible as you can.
Honestly, getting lit before you watch it is the ONLY way that Jaws 3 is even bearable.