This urinal belongs to a restaurant that, at the time, was running a special that came to $10.79. That isn’t unique – $10.79 is $9.99 plus tax – but thanks to that special being popular, more customers were getting 21 cents back as change. From that we can extrapolate this guy’s thought process:

“I hate change. What to do with it? … Leave it for someone else, maybe. But what does that do for me? … Maybe I’d get a little pleasure out of making someone grovel or crawl for this 21 cents. But how to go about that? And man do I need to take a piss…”

I’m somewhat reminded of this:

…the differences being that that asshole at least had the spinal fortitude to demean another man to his face, and (adjusted for inflation) he was spending dozens of times as much money to do so.