It's easy. There are some few steps if you want to watch a movie with your mouth. Let me list them down for you.

- Repeat whatever the narrator/character of the movie says.
- Ask someone next to you (or possibly to yourself) on what happened/ how does it happened/ why did it happened?
- Answer you phone call loudly
- Answer your sms...loudly
- Tell the person next to you what is going to happen next
- Tell the person next to you how it happened
- Tell the person next to you why it happened
- Ask stupid yet obvious question
- Guessing who's the villian if you are watching a mystery
- Guessing who's the killer if you are watching thriller
- Sing thriller
- Shout "I love you" to Leonardo Di Caprio out loud
- Curse loudly when you're shocked
- List down your critics while watching the movie

I had a lot of experience when it comes to "noisy movie goers" situations. Once when I was watching Harry Potter's first movie (back then I read the books) and this young Indian girl kept on telling her parents on what is going to happen. Sheesh. I read the book also man.
The latest would be when I was watching Spiderwick Chronicles. Will tell you later on the next update.