Green’s Dictionary of Slang

1. (also shims) a male homosexual.

1985

T.R. Houser Central Sl. 47: shims A sissy or homosexual.

2. (US black) a lesbian; a masculine-looking woman.

1972		B. Rodgers Queens’ Vernacular.
1982		Maledicta VI:1+2 Summer/Winter 133: Here are some obsolete or nearly obsolete terms which careless lexicographers continue to list as current […] shim.
2000		Ebonics Primer at www.dolemite.com 🌐 shim Definition: a manly woman Example: That shim armpits look like she has Buckwheat in a headlock.

3. a trans–sexual.

1979		E. Torres After Hours 188: ‘Where do I come in?’ ‘That’s what the trick said to the he-she.’ ‘You mean the shim.’ He slapped skin again.
1999		Roger’s Profanisaurus in Viz 98 Oct. 25: Shimsn. See ladyboys.
2013		T. Pluck ‘Story of O Street’ in Life During Wartime (2018) 58: [T]hey came to Times Square in droves, looking for shims. Not a she, not a him. A little of both.