At the party when Fat Albert raps and sings in front of the crowd.
When Reggie tries to kiss Doris to get Lauri jealous, Doris tries to tell him to stop but he won;t she she runs off crying. Seeing this, Rudy goes to Reggie and says, "Hey, man, you're like no school on Saturday, no class!" Fat Albert tells Rudy to check on Doris and then proceeds to tell Reggie complete with the eyebrow, "Stay away from her, or you'll have to deal with me." Reggie turns away, but finds all the gang staring at him and also, everyone else at the party.
Which gets even better later on. Fat Albert came to the run meet to cheer Doris on, but seriously risking his life in the process, as he's almost completely faded by this point. Reggie and his friend/henchman had spotted the secret earlier (That FA is a cartoon character) and appeared to have a plan, while Doris and Lauri try to get a drained of energy Albert back to the TV. Reggie confronts them, and it looks like he's going to spill the beans (and even starts to do so)... but then Albert, who can barely walk at this point, picks him up by the collar, pulls him close, says "Hey hey hey, get out of my way" and throws him off to the side, causing Reggie to simply run away.
The Original Cosby Kids (including Bill) visiting Albert Robinson's (Where Fat Albert got his name from.) grave and running off to play like they used to.