Green’s Dictionary of Slang

(Aus./US campus) an aggressive critic.

1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 21: Bagger Castigator.
1992		M. Coleman Fatty 105: ‘Bozo was a shocking bagger. He’d give everyone a hard time, but it was done in fun’.
1997–2002		Hope College ‘Dict. of New Terms’ 🌐 bag on v. tr. The act of picking on someone or something. College-age males who tease others are likely to be the biggest ‘baggers’.