The act of having sexual intercourse in the back of a U-Haul truck while surrounded by stuffed walruses and fuzzy pink dildos.
Grandpa: Hey sexy lady I got a U-Haul, wanna mook?
Grandma: I was hoping you'd ask! I'll get the fuzzy pink dildos.
Grandpa: Okay I'll be waiting in the truck to start mooking!