Green’s Dictionary of Slang

(US black) moody, changeable, inconsistent, indecisive.

1946		Mezzrow & Wolfe Really the Blues 218: Man she’s too some-timey, she will and she won’t, she do and she don’t.
1955		G. Taber Stillmeadow Daybook 136: That Becky is sure sometimey. [...] I am a sometimey person too. Sometime I like to be alone and listen to the sound of leaves about to fall.
1967		M. Braly On the Yard (2002) 249: They’re sometimey bitches. Sometimes they show, sometimes they don’t.
1972		D. Claerbaut Black Jargon in White America 80: sometimesy adj. inconsistent in one’s personality; moody.
2002		‘Touré’ Portable Promised Land (ms.) 59: Sometimey (Adjective) ‘You never know whether she’ll show up or not. She’s so sometimey.’.