Vince McMahon -- CAUGHT SHARTING ON SMACKDOWN ... Says Jim Ross

WWE honcho Vince McMahon accidentally dropped a powerbomb of his own during a taping of "Monday Night Raw" ... sharting himself in KHAKI PANTS right before a live segment ... so says Jim Ross.

Ross was dishing on his former boss' "Al Roker" moment during an interview on the "Opie & Anthony" radio show ... saying Vince was trying to jokingly fart in a producer's face ... when his plan backfired, literally.

"It got liquid," Ross said ... "He sharted."

And how did everyone know? Jim says it stank ... plus, the evidence was splattered all over Vince's khaki pants.

As The Rock would say ... Can you SMELLLLLLLLLLLLL what McMahon is cookin'?