EXCLUSIVE

Anthony Weiner's sexting partner Sydney Leathers is living up to her last name ... in the most disgusting way possible -- TMZ has learned she's slicing off a portion of her hoo-ha ... and auctioning it to the highest bidder.

Sources tell us, Leathers' recent foray into the porn biz made her self-conscious about what she calls "excess skin" down there -- so she's decided to undergo a labiaplasty ... to remove a portion of her outer genitalia for a "cleaner" look.

We're told Sydney's getting trimmed next week in Santa Barbara with a doctor named Neal Handel, and it's gonna cost her $8,400. Those porno profits (yeah, she had some) will come in handy.

The really gross part ... we're told Leathers plans to SELL the surgically-removed skin on an auction website.