When I had my net send fun back in school, an IT guy found me and just explained that if it becomes a recurring thing, they'll have to disable it on the network. And that they would prefer to keep the functionality available, so it would be a real shame if I ruined that for them. I never did another one, because I understood it would be a dick move.
No condescension, no threats. Just treating me like an adult with a constructive conversation. It never occurred that anyone might overreact like many in this thread experienced. Makes me feel pretty fortunate now.