When I was in primary school (grade 4 or something), we had a hard-arse disciplinarian for a teacher — the kind that would hold the whole class back for something that one person did, and would routinely give out 100 lines ("empty cans make the most noise" was his favourite) for the most pathetic little things.
Anyway, right from the start of the year, he decided to make it a rule that we weren't allowed to push up our sleeves on ours jumper (which as the fashion at the time), and he'd give out lines or whatever to students who did it.
One day, pretty much the whole class decided to push up their sleeves when we came into class and to do so every time we came back from recess or lunch, no matter how much we got punished.
We were united and we were unmoving, and after a few days, he gave up and stopped trying to punish us for it. We had a minor victory over The Man!