Green’s Dictionary of Slang

wetty n.

(Aus.) a disappointment.

1914		Sport (Adelaide) 7 Aug. 4/5: Bewster has got two fine wettys — Doc and jerry .
1960		A. Buzo Front Room Boys Scene i: Barry Anderson’s already had one wetty today, so let’s keep him happy, all right?

In phrases

have a wetty (v.)

(Aus.) to work oneself up into a rage.

1968

A. Buzo Norm and Ahmed (1973) 17: Eh, come on Ahmed, now don’t have a wetty. No offence meant. You’re not angry, are you? Eh?