My personal favourties are 2 and 6.
1. Stand up halfway through the movie and yell loudly, "Wait... where the hell is Harry Potter?"
2. Block the entrance to the theatre while screaming: "YOU SHALL NOT PASS!" - After the movie, say "Lucas could have done it better."
3. Play a drinking game where you have to take a sip every time someone
says: "The Ring."
4. Point and laugh whenever someone dies.
5. Ask everyone around you if they think Gandalf went to Hogwarts.
6. Finish off every one of Elrond's lines with "Mr. Anderson."
7. Talk like Gollum all through the movie. At the end, bite off someone's finger and fall down the stairs.
8. Dress up as old ladies and re-enact "The Battle of Helms Deep" Monty Python style.
9. In TTT when the Ents decide to march to war, stand up and shout "RUN FOREST, RUN!"
10. Every time someone kills an Orc, yell: "That's what I'm Tolkien about!" See how long it takes before you get kicked out of the theatre.
11. Talk loudly about how you heard that there is a single frame of a nude Elf hidden somewhere in the movie.
12. Start an Orc sing-a-long.
13. Come to the premiere dressed as Frankenfurter and wander around looking terribly confused.
14. Imitate what you think a conversation between Gollum, Dobby and Yoda would be like.
15. Release a jar of daddy-long-legs into the theatre during the Shelob scene.