Hmmm. That's a toughie. It's probably a Steven Seagal but... so bad it's good kind of bad.
OK, yeah I'm going to go with Under Siege. The break dancing scene and his bro banter with some barely intelligible rapper dude are off the charts bad.
I'm thinking of someone else, maybe a different Seagal movie. Dude was like a rapper / standup comedian. Younger, had hair, acted ridiculous but dangerous AF. I think he was meant to be a gang banger.
There are various forms of worst, of course. I walked out of Pasolini's 120 Days of Sodom because I thought it was sexually delinquent self-indulgence in disguise. I walked out of The Running Man, too, because it was just really shit. I stayed to the end of The Incredible Melting Man, agog at its transcendent ineptitude. "My god! It's his ear!"
I had no problem watching 120 Days, because I thought it was an exposition (perhaps exaggerated, perhaps not) of fascist depravity (or as Wikipedia more fulsomely puts it, "explores the themes of political corruption, murder, abuse of power, sadism, perversion, sexuality and fascism."). OTOH I found the mass murder church scene in Kingsman Secret Service to be gratuitous, OTT and serving no valid purpose. Plus it was overall a shitty movie.
Not to mention that each genre is more than capable of putting out dross, which can be difficult to compare to others.
I'd put Mercury Rising up there just because it's bloody awful and I've never forgiven the friend who recommended it and Hostel, which was just gore porn and had no reason for being made beyond this.
The worst film I've ever seen is Forrest Gump. My reasoning is that it's clearly the worst film ever made. Some people feel it has redeeming features, but this is not the case.
Not trolling. I absolutely hate it. I can't think of anything good about it whatsoever. Film "ideas" that were far better done by Zelig and Being There. The laughable notion that the American Dream is so wonderful that even the disabled and disadvantaged can fly to the top. The portrayal of every single character to the left of Jo McCarthy as flawed and doomed. The criminal waste of money in making this shit.
I wasn't disputing that you hated it, more that you may have been taking the piss out of the vague reasons for disliking other films that we've had in this thread already. :-$