Larry Csonka celebrated the Steelers' loss like a BOSS on Monday ... breaking out a stogie and booze after Washington helped ensure the 1972 Dolphins would remain the NFL's only undefeated team for at least one more season.
"Tonight, I'm a Washington fan!" the legendary Miami running back said as he puffed his cigar.
Of course, Csonka and other Fins players from the '72 team that recorded the NFL's only perfect season have made it an annual tradition to throw a little party every time the league's last unbeaten loses.
Usually it's a petty tweet or somebody poppin' bubbly .