When something you like happens that you want to celebrate.
Bungshung! I got 10 out of ten in my exam today!
To throw a nancy.
To have a tantrum.
To have an argumentative strop with someone.
Eddy: Fuck you! Alright!
Bill: Ooo! Eddys throwing a nancy!
EG2:
Freddy: I want a hotdog!
Doug: Oh, dont throw a nancy, freddy.