Most people aren't paying any attention to you at all. Unless you're being loud or making a lot of quick movements they probably don't even notice you beyond the generic recognition that another person is present.

As long as you aren't talking to yourself loudly in the theater or eating popcorn at a volume comparable to the Dolby, literally nobody will fucking care. In both cases, the solution is to close your god damned mouth.

I go to restaurants, concerts and other shit by myself all the time. I go some Sporting events by myself, even out of town. In fact, I'm going to take a nostalgia road trip and watch an indoor soccer match.