I've seen my share of horrible movies, but I can narrow my list down to these:
"North Country" - I had to watch this abomination in a class in college. The movie was so bad, I either drew, worked on a cross word puzzle or tried to ignore it. The movie eventually got so bad, I walked out of the classroom! (The teacher wasn't there, though. She had a family emergency to take care of.) I never want to see that movie again!
The entire "Spy Kids" trilogy or series...whatever that was. The first one was corny, the second one was worse, and the third one was so bad, I had a headache for a good couple days! (Glasses on, glasses off. Lather, rinse, repeat.) I could write a better trilogy than that in my sleep!