Everyone thinks of the Cosby show as this clichéd idealized family. However from the first episode it was actually somewhat groundbreaking in that the dad could be cranky and the kids could be screw ups.
I remember watching the first episode of the Cosby show. And when Theo made the speech about failing in school and how he hoped his father would still love him, everybody in the audience was waiting for the then Cliched sitcom hug.
Instead, when Cosby said 'son that is the stupidest thing I've ever heard,' both the studio audience and everybody at home went nuts. Because that was exactly what a real dad, not a television dad, would say.