Every reality show on the planet should give up NOW -- because the girls on TLC's "My Big Fat American Gypsy Wedding" just set the record for the wildest, most ruthless catfight of all time ... and it was all caught on tape.

The fight went down last November at a "gypsy" wedding in West Virginia -- the smaller girl (Mellie) hails from the groom's side and the bigger girl (Diamond) was the maid of honor.

Sources tell TMZ, neither side of the family exactly approved of the union -- but Mellie took it one step further after the ceremony ... running her mouth about how the bride and groom don't belong together.

Diamond caught wind of it ... and FLIPPED -- shoving Mellie to the ground outside the church.

At that point, both girls unleashed fist-flying hell -- beating the living crap out of each other and pulling at each other's clothes until they were naked ... literally.