Today's sex term is slang from the UK:

how's your father--which means to have sexual intercourse. It is an older slang term, by no means cutting edge, yet it's still used by some and understood by most. Proper usage adds "a bit of" to the term, so you end up with "a bit of how's your father," or "I just stopped by for a bit of how's your father" or "What's that noise? Well, Mary and Bob went upstairs for a bit of how's your father..."

The origin might have been a World War I song that soldiers liked to sing.

Related slang expressions used in the UK might inlcude: to ride as in "have a good ride", a legover as in "to get a leg-over", to have as in "Did you have him after the party?", also shag, grind and the other usual suspects.