boo-boo, n.³ — Green’s Dictionary of Slang

boo-boo n.³

[? Yid. bulba, potato. Major, Juba to Jive: A Dict. of Afro-American Slang (1994), suggests link to Bantu mbubu]

1. (US) usu. in pl., the testicles.

1951		T. Capote Grass Harp 67: Catherine said, ‘In the booboos. Collin, kick his old booboos.’ So I did [W&F].
1966		Trimble 5000 Adult Sex Words and Phrases.

2. (US gay) an erection.

1972

B. Rodgers Queens’ Vernacular 103: erection [...] booboo.