Similar to what KOAB said. If it's "one of those movies" that warrants a commentary, jokes, etc. than I have no problem with it.
If it's something more serious or something that I want to be able to pay attention to then they get the "shut the fuck up" treatment from me. Which is wierd, I must be really touchy because I am almost always the only person in the theatre who'll say something.
To add on to that, I hate it when couples bring their kids to movies that kids have no business being at. Especially if they're under 4 years old. When I went to see Land of the Dead, this woman brought HER TWO YEAR OLD CHILD into the theatre with her. The entire crowd burst into a cheer when she was finally asked to leave and she belted out "FUCK YOU!" - Ahh priceless memories.