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1.
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.
Man1: "DUDE!!!! So guess what I did last night!"
Man2: "...what?"
Man1: "I sucked my own dick!"
Man2: "WHOOOAAA SHIT BRO!!! YOU DID A NAKED SIT-UP?!?!"
Man1: "Fuck yeah!"
Man2: "OH MY GOD!!! TEACH ME YOUR WAYS!"

Girl1: "Ew! So last night I walked in on my brother trying to do the naked sit-up."
Girl2: "EWWWW!!! That's like sooo gross, like oh my god... ew."
by zoee-owee-owee September 18, 2010