fink on (someone)
To report someone's misdeeds to an authority figure. The gang was determined to find the traitor who finked on them to the police. How could you fink on me to my parents? Now I'm grounded for a whole month!
fink on someone
Sl. to inform parents, the authorities, etc. on someone. You're not going to fink on me, are you? Chuck finked on all of us.