naked sit-up

The act of performing fellatio to one's self as a form of masterbation. More properly and politely referred to as self oral or autofellatio.

It is physically possible for men who have sufficient flexibility or penis size or a combination of the two to perform the naked sit-up.
Statistics show that every 3 out of 1000 men are capable of it.
The naked sit-up was given its name because when one tries to perform it, it looks as though they are trying to do a sit-up (and usually failing stupendously) while naked.
It is rumored that Marilyn Manson had his botton two ribs removed to be able to do the naked sit-up.