regular game of 500

Code for a mature aged orgy and/or dogging meet up. Was a popular term in the 70's and 80's, but has lost its meaning with the younger generation.

Used now days by mature aged swingers who are no longer lithe, supple or limber enough to answer the call to a normal orgy to hip or spine injury's, heart and lung disease, and clotting disorders etc etc

Wife to her husband: "Let's invite the new neighbours over for a regular game of 500" (winking her eye)
Husband to Wife: "Sounds like a fantastic idea, I will lay the plastic sheeting down now!"