If you've seen the film, but your mate hasn't, don't explain the plot, don't give away major surprises, and don't nudge ribs. If you hear a funny line, don't repeat it. If you're watching a Bertolucci, Coen Brothers', or David Lynch film, don't ask questions. Let art flow over you. If you're gonna sneak in a beverage, don't bring it in aluminum cans.
Nachos make bad movie food.
By the end of the first reel, your lap will be a kiddie pool of luke-warm cheese dollops. Burnt umber equals bad. If the snack bar attendant asks your butter preference, don't finesse it. Remember, this is the same locale that sucks your shoe soles tighter than a kitten on a tabby titty. It just ain't done.