Jason Kelce Does Bowling Ball Shot At Bills Tailgate

Jason Kelce's job is pretty sweet -- the future Hall of Famer was back to his tailgate shenanigans ahead of "Monday Night Football" ... partying it up with the notoriously rowdy Bills Mafia!!

Former Buffalo center Eric Wood documented the debauchery ... showing the Philadelphia Eagles legend -- sporting a Fred Flintstone costume and Bills-themed hat -- doing a shot of Gatorade out of a bowling ball.

Of course, the stunt is common prior to Bills games ... as well as a bunch of other wild antics like assaulting innocent tables.

Kelce -- who vowed not to drink alcoholic beverages before hopping on the ESPN mic -- joked he hoped someone "snuck something in there" ... but as long as the contents of the bottle were as advertised, he won't be slurring on the "Monday Night Countdown" desk.

He cleaned up pretty well ... as he ditched the Fred 'fit for a Bills-themed suit (complete with chicken wing chain) as he made his way to the TV set.