Ronnie Lott -- Aaron Rodgers Should 'Man Up' ... WEAR 49ers JERSEY!!!!

Green Bay Packers QB Aaron Rodgers needs to "man up" and stop trying to weasel out of the bet he made with Boyz II Men ... this according to NFL Hall of Famer Ronnie Lott.

Lott is no stranger to friendly wagers -- the 49ers legend tells us he used to make similar fun bets with Huey Lewis back in his playing days ... and would always HONOR them when he lost.

And since Aaron lost his bet with B2M -- and should have to wear an Alex Smith 49ers jersey -- Lott tells us the QB needs to pay up soon ... or else it could haunt him later in the season.

“I have a feeling it will bother him the next time he plays the Niners. If they meet again this season, it will bother him.” SF and GB aren't scheduled to play against each other during the regular season -- but many expect them to face off in the NFC Championship game.

Lott tells us he wouldn't be surprised if Boyz II Men gave Rodgers a shot at a "double-or-nothing" bet later this year to clear his debt.