A Fink
A fink is someone who’s so messed up they think telling on you is the best way to win. They’re like a brain-dead chicken who just doesn’t know what to do.
He was a fink and told the teacher I was talking during math.
That fink was so dumb he told on me for eating a donut.
She was a fink and told on me just because I didn’t let her sit with her friends.