I'm quite a snob with my free time, so I tend to at least get a steer for what I'm watching before I spend time watching it. There's probably a load of films I saw as a kid which were terrible, but I don't remember any specifically making me feel bad.
However, I did find Transformers 2 to be terrible. Dumb action, dumb story, too long, horrible humour, shot like soft porn any time Meghan Fox is on screen. No. Just no.