Green’s Dictionary of Slang

(US juv.) excrement.

1960, 1975		Wentworth & Flexner DAS.
1966		H.S. Thompson letter 25 Dec. in Proud Highway (1997) 596: Not the boom-boom bullshit of the [...] Sam Huff films.
2024		Bluesky 6 Dec. 🌐 [I]t’s pathetic how these supposed alpha men need their mommies out there cleaning up the messes from their little boys who tried to make boomboom in the potty and shat themselves instead.