They call him the G.O.A.T. ... they should call him the H.O.R.S.E. ... 'cause according to Jerry Rice, he's hung just like one.
The Hall of Famer appeared on "Watch What Happens: Live" with Andy Cohen this week when he was asked to spill his guts about the biggest penis he ever saw in an NFL locker room.
His answer -- "He's sitting here."
Check out the look Giada De Laurentiis gives him right after he says it ... priceless.