I have known one guy who could do it. He showed me (with clothes on). He had to have a double-jointed back or something because it was a position no human should be in. The weird thing is he wasn't otherwise extra-limber or anything. *shrug*
Mmm. I used to be able to put my feet behind my head & do splits all the way down, etc. I might have been able to do it many years ago, but I was too young at the time to care.