to attack someone's ass while their pants are down and they can't defend themselves. Often for the amusement of others.
2. I rode my unicycle to the sea and took a swim today. By the time I got back home (it was 30km there and back), picked up some groceries, scrubbed off the sunblock, prepared a green salad and steak dinner, and washed it down with a glass of Chianti, I was absolutely spanked.