Diddy & Ashanti -- Fur-Ballin' During Late Night Grub Run

Diddy was clearly overdressed during a pre-Super Bowl visit to a landmark greasy spoon in Harlem.

We're told Diddy -- and his 15-person entourage that included Ashanti and French Montana -- rolled up at around 3 am to a famous outdoor food stand called O'fishole Sea Food -- long known in the hood by its previous name -- Willie's Burgers.

After ordering at the walk-up window -- 5 orders of cheeseburgers with fries and 3 fish and chips -- we're told the group created quite the spectacle as they sat on a brick wall and chowed down.

Ashanti left a $100 tip ... on a $40 bill.

The manager tells TMZ, "Coming here is the hood thing to do."

The decent thing to do ... stop wearing fur.