Slim was the counterman at Slim's Malt Shop, which was the alternate version of Chubbie's Famous when Cory was transported into the 1950's in I Was a Teenage Spy. Unlike Chubbie, Slim seems hostile to the kids who were dancing in his restaurant, calling them a "zoo full of weirdies" and demanding that they return to class in school.
He is not too friendly to Cory, asking him if he "flipped his wig" when Cory asks him what the year is.
Although the character is credited as "Counterman," he is addressed as "Slim." Therefore, the title "Slim" is considered non-canon.