Green’s Dictionary of Slang

charlie n.¹⁰

(US) the penis.

1970

J. Bouton Ball Four 163: If you get caught eating at the table with Charley uncovered, that costs a dollar.

In phrases

introduce charlie/charley (v.)

to have sexual intercourse.

1997		A. Wallace ‘The Listress’ Salon.com 16 May 🌐 What activity are the following euphemisms for? 1. Eat cauliflower. 2. Wind up the clock. 3. Drive home. 4. Have a Northwest Cocktail. 5. Introduce Charlie. 6. Parallel park. 7. Buzz the Brillo. 8. Make the chimney smoke. 9. Talk about Uganda. Answer: Have sex.
2000		Sex-Lexis 🌐.
2002		Shagnasty Penis Owners Club Presents... ‘Lots and Lots of rude words and phrases’ 🌐 FORNICATION [...] Introduce Charley.