Shaving. I was obstinate enough about it they ultimately gave up. A coach would pull you out of lunch and hand you a razor. Fuck that. I'm not doing it. What are you gonna do? Shave me yourself?
They put you in a tiny cubicle in a room where you do your work and nothing else in total silence for the entire school day. Or send you home unexcused.
My dad's trade school had this rule back in the 70s/80s. If you showed up and weren't clean shaven, you had to pay $0.25 for a disposable razor and small little pouch of shaving cream. If you refused, you were sent home for the day.
He had a teacher that he said was really well liked among the students, former Marine who I think served in Vietnam. The guy had a coconut carved into a monkey's head on his desk, and he'd tape a cigarette in its mouth. But he had some odd rules and, according to my dad, could be a scary dude at times.
Like, if he caught you yawning, he sent you out of the class because "You aren't full awake, and therefore didn't prepare for class properly with a proper night's sleep."
If the class got off track, or really pissed him off, he'd either:
A. Lift one of those old-school metal drafting tables off all four of its feet and slam it back down, causing a HUGE boom sound that got everybody's attention, or,
B. He'd drop-kick the coconut monkey head down the hallway before returning to the class.