I don't watch a lot of movies, and I'm as dumb as a sack of rocks; so I usually can't tell if a movie is bad or not unless someone outright tells me it's bad.
That being said, worst movie I've watched to completion was Hot Tub Time Machine. I just didn't find it particularlly funny and it didn't do anything for me. I don't hate it, just didn't like it either.
Worst movie I "watched" recently was Surviving Christmas. It's on HBO Now; It has Ben Affleck and James Gandolfini in it, and was made in 2004. I figured it was going to be something maybe light hearted? I didn't even get past the opening credits, because during the opening credits they have an old woman putting her head in the oven. That whole trying to be dark and edgy thing in an attempt to be funny is just ugh.