Note: Despite containing the term shag in it, sex is not necessarily part of a shagdown. It can be, of course.
Liam: Yeah, reckon it's time for a shagdown?
Valerie: Great race, told you I'd win!
Tom: Yeah, let's head back to the lodge for some shagdown.
Rupert: I'm bushed... gonna head to the pub for some shagdown, you coming with?