As a male nun you will avoid being detected by everyone, including your class mates and teachers alike. This is especially true if you wear your nun costume at all times and manage to restrain yourself from pulling your underwear down at random intervals.
Be sure to wear as much eyeliner as humanly possible. If anyone asks you to remove the makeup, tell them that Jesus made you do it and that if you were to remove it then Jesus would kick your ass when you finally reach Hell.
The best way to have fun as an Emo in Catholic School is to be overtly sexual. Call all of the priests “sexy chops”. Tell everyone that “Jesus looks like one Hell of a sexy hunk” and that “Mother Theresa makes my loins sweat like grease dropping off of a pork chop.”