Its axiomatic: people want to pay as little as possible. But there's a certain kind of consumer, who goes out of their way to flaunt that while they could pay more, they're not going to. And its not because the extra $10 for a reasonable tip would break them. Its not because they fundamentally disagree with the concept of tipping (although that may well be the case in addition). Its because the person "tipping" believes that no adult should be working at a movie theater, and if they wanted to make real money, they'd get a real fucking job, and no, I'm not taking resumes, why would I want to hire somebody who could only get a job pouring beers at a movie theater?!
Its really hard to overstate the antipathy that service sector employees experience on a regular basis, and how far out of their way certain customers will go to make sure that those employees know that those certain customers hold them in utter contempt.