Semi-OT: Worst movie you've endured in a theater

What's the worst movie you've sat through first-run at a theater, and why? Walk-outs don't count because you didn't experience the full awfulness of it (I've never walked out).

I made this "semi-OT" because for many, this would be a horror movie. For me, it's not a horror movie, but a movie by one of the greatest horror directors -- Cronenberg's Cosmopolis. One's reaction to the movie would probably be colored by whether you read the dreadful Don DeLillo novel beforehand, which I did. The book is bad in its own right, just a negligible modernist literature wet fart. Nothing about it, though, lends itself to a cinematic adaptation . . . nothing. This is the problem with adapting books such as this -- you have dialogue and situations which work (or don't work) being read, but not being said. What Cronenberg obviously did was open the book at his computer and just transcribe it, no imagination or attempt at adapting. So what you have is a novel that's lame in its own right, filtered through into a bland film where the actors are speaking dialogue meant for a novel only.

Aside from that, Robert Pattinson is just like a "nothing" on screen. The worst actor, though, is Paul Giamatti in his smaller role. I've never liked him; he just grates on me. In this he is almost unwatchable as he yells the book dialogue. The whole film was just a terrible cinematic experience.

Some runners-up (or runners-down?) for me:
The Lovely Bones (Peter Jackson)
Interstellar (Christopher Nolan)
The Aviator (Martin Scorsese)
Hugo (Martin Scorsese)
The Curious Case of Benjamin Button (David Fincher)
Diary of the Dead (George A. Romero)
The Counselor (Ridley Scott)
The Revenant (Alejandro G. Inarritu)
Lady in the Water (M. Night Shyamalan, and Giamatti again!)
My Soul to Take (Wes Craven)
Valentine (Jamie Blanks)
Away We Go (Sam Mendes)
Inherent Vice (Paul Thomas Anderson, and this has some of the same problems as Cosmopolis.)
I Still Know What You Did Last Summer (Danny Cannon)