Green’s Dictionary of Slang

intercourse under the armpit, generally a homosexual practice.

1785		Grose Classical Dict. of the Vulgar Tongue n.p.: Bagpipe, to bagpipe, a lascivious practice too indecent for explanation.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1972		B. Rodgers Queens’ Vernacular.
1989–2003		R.O. Scott Gay Sl. Dict. 🌐 bagpipe: Sexual intercourse performed on the armpit of a partner until an ejaculation is reached.
1999		Hip-Hop Connection Dec. 45: ‘Buddy’ which involved Jimmy, Jenny, troilism, bagpiping and ball torture.
2000		Desdemona at www.asstr.org 🌐 Cherry knew before she was ten that a nooner was sex in the afternoon. And by twelve she could explain that bagpiping was a man fucking your armpit, and knee-tremblin’ was when you had sex standing up.