Anything on TV or a streaming service or device doesn't count. It has to be a god-awful movie you went out to a movie theater to watch.
For me, it was one of two movies I went to see while I was still in high school. The first, and the worst by far, was The Swimmer, a 1968 movie starring Burt Lancaster. The plot, such as it was, dealt with a rich white man who swam his way home through the pools in the adjacent backyards of his wealthy Westport, CT neighbors, and the interactions he had with these fascinating characters. It's difficult to express in words just how much this movie sucked. It was so unremittingly bad that we sat through it, assuming, then hoping, that something interesting would eventually happen. It didn't.
The second and nearly as bad, was Five Easy Pieces, a 1970 movie starring Jack Nicholson. Like The Swimmer, this was another artsy-fartsy character development movie with even better critical reviews. Nicholson's character is a California oil field worker who is basically an asshole. He has a waitress girlfriend he knocks up and a married best friend he gets drunk and goes out whoring with and who gets arrested for robbing a gas station. Bobby (Nicholson) never tells these simple folks he is a former child piano prodigy from a wealthy family of musicians. When he finds out his estranged (naturally) father has had multiple strokes, he reluctantly journeys to the family domicile, with his girlfriend tagging along, much to his chagrin as he is embarrassed of her in front of the family. After multiple scenes of strained family dynamics, including Bobby screwing his older brother's fiance, he abandons everyone, including his pregnant girlfriend, to continue his voyage of self-discovery and rejection of bourgeois values. The movie ends with him hitching a ride on an 18-wheeler headed for Alaska. This movie also completely and totally sucked. Astoundingly, both Nicholson and Karen Black who played his girlfriend, received Oscar nominations.
So those are my worst of the worst. Both cost me roughly 2 hours of my life I can never get back.
What were yours?