Green’s Dictionary of Slang

gloom n.

(US) a depressed and/or depressing individual.

[1796		in N.E. Eliason Tarheel Talk (1956) 274: Their daughter has eloped [...] it has the appearance of [...] glooming the Father for life].
1915		D. Lowrie My Life out of Prison 212: You’re getting to be a regular gloom.
1920		F.S. Fitzgerald This Side of Paradise in Bodley Head Scott Fitzgerald III (1960) 79: ‘I’ve got a class at eleven-thirty.’ ‘You damned gloom!’.
1930		W.S. Maugham Bread-Winner Act I: Oh, God, you are a gloom, Judy.
1932		J. Dixon Free To Love 112: He is, my precious old gloom, but why bring that up?
1932		‘R. Scully’ Scarlet Pansy 345: She is gay, not morose, not a gloom shedder.

In compounds

gloom bug (n.)

a depressed individual.

1923

T. Boyd Through the Wheat 55: Come out of it, you gloom bug.

In phrases

gloomed up (adj.)

(US) depressed or depressing.

1919

H.C. Witwer Smile A Minute 27: It helps take people’s mind off of the war and prevents ’em from bein’ all gloomed up.