3
If he's doing it in your presence, report him to Title IX for sexual harassment. If he's doing it in his own room, then it's none of your business.
Yell this. Very loud. “IF I EVER EVEN FEEL LIKE YOUR DICK IS IN THAT HAND WHEN IM HERE, I AM GOING TO BEAT THE SHIT OUT OF YOU TILL YOU CUM”
Join in. Bring the rose toy