Green’s Dictionary of Slang

describing a person who enjoys giving oral sex, thus go-down man, go-down girl.

1963		J. Rechy City of Night 115: Hes a go-down fruit serviceman.
2021		J. Ellroy Widespread Panic 99: ‘I’m the Lizard of Love [...] a go-down man from way back [...] Your wife rings my bell eight nights a week. She’s a go-down girl from way back’.
2023		(con. 1962) J. Ellroy Enchanters 45: ‘Go-down guy — not bad’.