Yeah well, banning of a three inch blade isn’t really an American custom, I think. Nor is it an American custom to expel pupils for drawing a gun, or any of the other bizarre PC nonsense.
Custom and idiocy in retard groups are different things.
It may not be "custom" but it is the law. No folding blade over 3 1/2 inches and no nonfolding blade over 2 inches. Case law, with precedents.