I wouldn't say it's a myth. It's been a while but I recall being in a theater (San Luis Obispo, CA) and witnessing a manager ask a person to throw away his smug

I wouldn't say it's a myth. It's been a while but I recall being in a theater (San Luis Obispo, CA) and witnessing a manager ask a person to throw away his smuggled snacks or leave the theater. He declined to do both and the police arrived and escorted him out.