A puppy pile is when a group of inebriated adults decide it's a better idea to jump in the closest bed available, with whatever lack of clothing they still have on, and cuddle like a pile of puppies, until sobriety catches up with them, and they individually sneek out the back door.
*drunk in hot tub*
'Leona' - "we're out of beer! Let's go make a puppy pile!"
'JoJo' - "That sound's amazing! What's a puppy pile?"
'Leona' - "You, Z, your husband and I go crash in you'r bed!"