Green’s Dictionary of Slang

all there but the most of you phr.

[all is the genitals, the most is the rest of the body]

having sexual intercourse.

1890
1890190019101920193019401950196019701980
1984
[UK]Farmer & Henley Sl. and Its Analogues.
[UK]Partridge DSUE (8th edn) 15/1: [...] mid-19C–20C.