Every ragamuffin that has a coat to his back thrusts his hands in the pockets, rolls in his gait, talks slang, and is an embryo Coachey.
"The Sketch Book of Geoffrey Crayon, Gent." by Washington Irving
One of our men, a young fellow from Dera Ismail, jumped on the wall to slang 'em back, and jumped down, blubbing like a child.
"Stalky & Co." by Rudyard Kipling
The term derives from the use of moon or moons as slang for the bare buttocks, a usage that dates back as far as the 18th century.
So forget about the sinister slang expression that you may have learned on the back of the school bus during your wonder years.