INSANE SUMO HIGHLIGHT -- Fat Guy In Diaper Slams Other Fat Guy In Diaper

It's possiby the greatest Fat-on-Fat takedown of all time -- an XXXXL SUPLEX at the U.S. Sumo Open in L.A. this weekend ... and it was all caught on tape.

The Slammer -- Byambajav "Byamba" Ulambayar
6'1", 346 lbs ... and the reigning U.S. Sumo Open champ

The Slammee -- Kelly "Big Tree" Gneiting
6'0", 420 lbs ... and pink diaper enthusiast

The two clashed in the sumo circle on Sunday ... and the slam was so ferocious, some spectators say they could feel the fat shock wave ripple through the stadium.

Sumo Fun Fact -- Byamba, of Mongolian decent, is 59-1 in his sumo wrestling career.

The one loss? Unclear. Probably some other fat bastard ...