Narker means that you're calling the cops. You are telling cops something about someone else trying to get them introuble. You're listening in waiting to get information. You're an informer for the authorities.
You're a fuckin nark. Are you a nark or what? Pussy narker. That's so narky. Be careful he's using narketry. Nark! Dude get away from those narkers. Oh man the people are just narking us we should bounce.