Since I can't seem to edit my original post (why? too long since I made it?), I'll ad here another movie I remembered watching:
- One Night Stand - 2 couples, make-your-own spin
This movie portrays how stupid it is to abide by the social hangups about sex outside marriage. In the superbly ironic scene at the end, the wife of one couple A ends up having sex with the husband of couple B, while his wife B is having sex with the husband of couple A, in a perfect cross-couple affair, behind everybody's back, cheating on each other.