I think this could make for an entertaining thread: How old were you? Where were you? What was the title? What was happening in it? What kind of pizza were you eating?
For me, I was 17. I was over my buddy's house in the basement. The title was "Udderly Rediculous". It was a compelation of small bits and pieces of other porn flicks. The first scene was a parody to the Johnny Carson Show. I don't really remember much in terms of positions, etc, but I don't think I can forget the guy (trying to play Ed McMahon) saying "You are erect, sir!". I definitely had Papa John's.