It happens to the best of us, not much you can do. The next time it comes on just flip to another channel...
I watched South Park and I'm only thirteen. I have been scarred. How do I forget and forgive myself?
if you're not embarrassed, you could talk it out with someone. For me watching other movies, listening to music, and exercising help to flush old information out. It really just takes time. When you're older you may even enjoy that movie.
It's alright your only human, you'll be alright.