"look like a Flintstone"?

Not that I've heard. At least not until now. It's a look, though (think Fred and Barney, rather than Wilma and Betty).

It's a reference to the 5-o'clock cartoon shadow that Flintstone men have. Homer Simpson has the same thing.

I have a friend who gets 5 o'clock shadow by 11 AM. I would often tell him on days that he didn't shave that he had the "Barney Rubble Look"; I just liked how that sounded.