Pittsburgh Steelers -- Partying with Louis XIII ... $3,000 Per Bottle!

Nothing heals the pain of a loss like a $3,000 bottle of cognac ... just ask the Pittsburgh Steelers linebackers who busted out TWO bottles of Louis XIII at a Pittsburgh casino last night.

James Harrison, along with the rest of the LB crew, hit up Andrew's Steak and Seafood Restaurant at the Rivers Casino ... where they poured the cognac into fancy glasses engraved with their names.

Louis XIII is some of the most expensive cognac in the world -- right now, BevMo is selling the stuff for $3,000 per bottle (if you're a ClubBev member).

Seems the guys polished off the booze ... at least judging by the way they were singing and goofing around at the end of the meal.

Expensive hangovers ... still hurt.