The opposite of a happy ending when getting a massage. When you are so relaxed that you shit yourself during the massage.
Dana: Dude, I just had a great massage just now but I need to tip the masseuse big.
Eric: Why, happy ending?
Dana: Nope. Actually, it was the polar opposite. I was so relaxed I shat myself at minute 45.
Eric: Oh dude, crappy ending...