When a guy on the T starts swatting at your foot with a three-ring binder for no apparent reason

There is one of two possible explanations: He's just a T crazy or there's a cockroach on your shoe:

... Sure, it wasn't a full-sized one, but a cockroach is a cockroach and that thing was crawling on my foot?!OHMYGOD!

So the guy with the binder now goes from creepy weirdo to my savior as he stomps on the cockroach - a few times, for good measure. And now the world is burdened with one less cockroach. And I ... well, I'm paranoid outta my mind about them now.