Snitching is a game mechanic in Bully. It occurs when a student sees one or more other students misbehaving, and runs to tell an authority figure what they're doing. This forces the rule breakers to either stop what they're doing immediately and leave the area to avoid getting caught, or deal with an authority figure trying to bust them.
Only little kids and Constantinos snitch. All characters technically have the ability to snitch, and even have dialogue lines recorded for it. However, a character's likelihood for snitching is set to a meter, and most characters' meters are permanently set to zero, which means they have no chance to snitch.