Ah yes, Annoying Things People Do In Theatres. Loud munching of food and rustling of wrappers is infuriating, as is ice clinking loudly in drinks. I don't get how the person can't realise it's annoying, or how more people around them don't seem to be bothered by it.
People using their phones, talking... On a theatre message board I saw someone complain that the girl who came and sat next to them took her shoes off and put her sweaty feet up, stinking the place out. I've heard tales of people opening up containers of steaming hot food and eating it, including pizzas and even curry.