Back in the early 70s, my friend Wick and I were aboard a ship in the port city of Hobart. Wick decided to do a browneye (local lingo for mooning) out of a porthole. The porthole was some five feet or so from the deck and it took a considerable effort on Wick's part to leap, turn and twist to firmly insert his rear through the porthole.
Unfortunately, this caused some severe lacerations to Wick's nether region. The doctor at the nearby hospital had a hard time inserting the stitches because he was laughing so much :-)