I have to agree with Ant here. I work with film and have only recently realised that a lot of people I work with fucking hate popcorn in the cinema. Never even crossed my mind, I have more than enough being annoyed at people doing all of the things Ant has listed.
I did once tell a guy off for having a packet of crisps that he was munching away at, but a box of popcorn has honestly never bothered me.
Clean your mess up after yourself if you can’t eat it like a functional adult human being though innit