A fart fetish group has made an offer to ABC to license the rights to the infamous Nancy Grace "Dancing with the Stars" fart footage ... we repeat, a fart fetish group ... apparently, they exist.

A rep for the fetish site Clips4Sale.com tells TMZ, the company made an official offer to ABC yesterday -- writing, "After viewing and hearing Nancy Grace's alleged 'toot' after her performance on 'Dancing With The Stars,' [we] would like to acquire the rights of the three-second footage." (below)