Green’s Dictionary of Slang

1. (US) a leg [SE ].

1906

C. M’Govern Sarjint Larry an’ Frinds 65: Shake yer stand-ons, lad; ’taint so hellish late.

2. an erection [stand v.¹ on model of hard-on n.].

1958		(con. 1940s) B. Behan Borstal Boy 170: He couldn’t get a stand-on himself.
1993		(con. 1945) S. McAughtry Touch and Go 160: Let him slabber away there, sure anybody that needs to have the soles of their feet tickled before he can get a stand-on deserves nothing but sympathy.