Green’s Dictionary of Slang

(Aus./N.Z.) miserable, gloomy.

1917		A.G. Empey Over the Top 124: The Captain stayed about twenty minutes and came out. I couldn’t see his face, but the droop in his shoulders was enough. He looked like a wet hen.
1951		(con. 1941) E. Lambert Twenty Thousand Thieves 80: Dooley’s version portrayed Henry as almost in tears and begging forgiveness. ‘Like a bloody old wet hen!’.
1951		D. Stivens Jimmy Brockett 235: I felt as mopey as a wet hen and about four-thirty I called it a day and went off to the club.
2003		McGill Reed Dict. of N.Z. Sl. 136: mopey as a wet hen Glum and aimless. ANZ mid C20.