fart-narc
A fart-narc is a friend who will share unfavourable stories about you, usually in order to bring other people together.
More simply a fart-narc is a friend who will narc your farts.
More simply a fart-narc is a friend who will narc your farts.
“I love Tim but is the worst fart-narc we know. Don’t tell him your business or he’s gonna make you sound five times worse to anyone who will hear it.”