I once made the mistake of watching a movie with friends that are a couple, and they made out the entire time.... so I got up and left. They asked why I left and I told them the movie sucked.
For instance, I was at the theater last week and I did kiss the guy I was with several times during the movie. But it was like 3 kisses at best at a time. I wouldn't have fully made out with him because like others have stated, it's uncomfortable for others.