me ko pīwaiwaka
1. you're a nark, you’re a tattletale - an idiom likening someone to the fantail who laughed at Māui trying to enter Hinenuitepō causing her to wake and discover his plot to kill her.
Tama: Nā wai tātou i whāki? Hata: Nāku! Kei hē kē atu tēnei raruraru. Tama: E tama, me ko pīwaiwaka koe. / Tama: Who told on us? Hata: I did! Unless we get in more trouble. Tama: Oh man, you’re a nark.