(nark can also be spelled narc or narq)
1: To be a nark is to be someone that will report any misbehaving to a higher authority like the police, parents and teachers.
2: To nark, or to nark someone out is the action of reporting the misbehavior; also called narking.
3: To be narked is, obviously, the past tense of narking.
1: The other day I was taking some snoops and that nark ratted out on me!
2: I am so going to nark him for smoking that weed.
3: That bitch narked me out the other day for smoking the weed!