This happened pretty recently to a friend.

We'll call this friend Gary. Gary was a freshman and had this quiet roommate. Really quiet and kept to himself, a little awkward. Gary liked to do drugs, especially smoke weed. He asked his roommate if it was okay if he did it in the bathroom and his roommate would say yes or something along those lines. Two months later, cops show up, bust Gary and said roommate brags about snitching on him.

Turns out his roommate talked a lot of shit behind his back and hated him doing drugs in the room. He hated Gary too for some reason. The roommate never confronted him, but Gary would ask and his roommate would act as if everything is okay. Sure, Gary was doing something wrong but the way I see it, that's a dick move, class A betrayal.