The Love Champions

This movie is about a sex therapy camp where troubled couples go for counseling. So, the couples arrive, and the doctors and nurses help them with their love lives by teaching them how to pleasure each other, and the staff also joins in on the fun. The couples swing with one another, and the movie ends in a huge orgy, with lots of partner-switching.
The great thing about "Love Champions" is its sense of humor. The acting is too good for porn, and that's what makes it funny. They act out all the foreplay using naughty words while keeping a straight face. It's almost as if you're watching these people through a hidden camera instead of poorly staged-and-scripted lens.
But best of all, the movies great because it looks like it was made in the 70's. (I was really surprised to find out that it was made in 1985.) In the 70's, people looked really natural and they looked like they were really enjoying themselves, which really helps in this world of impersonal porn.