How does Mike O'Malley get to wear a cap all the time?

It seems like every time I've seen Mike O'Malley in a show, he's wearing a baseball cap. He wore a cap on those ESPN ads where he was "The Rick." He wore a cap on the crappy Mike O'Malley Show. He wore a cap on Yes, Dear (even when he got a job as a security guard, he got to wear a cap). And now I noticed that, on his My Name Is Earl guest stint, he was wearing a cap (when his character, Stuart, wasn't in his cop uniform... then he was wearing a police hat). Rich told me that his cap was off during the Earl episode, but it must have been quick, since I missed it.

It's weird, isn't it? I mean, I know why he wears the cap: he's bald as a billiard ball. And I've seen hatless photos of him on the Internet. So here's what I'm wondering: does he have "wears a ball cap" written into every role? Is there a clause in his contract that his character must wear a cap? Does he just wear hats out of what is probably a huge personal collection? Does he realize that this cap thing he's got restricts him to roles centering around slobs and baseball players (well, at least he'd be ready if he's ever cast in The David Wells Story)?

This is something that keeps me up at night. Well, that and global warming. But that cap thing... that the real head-scratcher.