The Flintstones is a cartoon, and it passed strict network standards in the conservative early 1960s, but that doesn't mean it's necessarily a show for children. This was a show about adults, for adults, and it catered to adults with episodes about adult problems. It also snuck in the occasional dirty joke, ones that grown-up viewers would understand but which would sail over the heads of the young and impressionable kids at home. (And, it would seem, the ABC censors.)
In one episode, Fred and Barney go to a costumer, and Fred asks Barney, "What kind of costume you gonna get?" Barney, a short guy, replies that he's looking for "something that makes me look tall." Fred cracks, "How 'bout another head?" and makes himself laugh. Barney's snappy and filthy comeback: "Another one? What do I need three of them for?" (See, he has one head on top of his body, and another one, uh, lower down.) Another time, Fred and Barney are watching sports on TV at the latter's house when they lose reception. Fred inquires if everything is in working order, including asking, "How's your antenna?" Barney replies, with a huge, self-satisfied grin, "Fine, friend, how's yours?"
It would also seem that they had "adult films" in the Stone Age, per a comment Fred makes in the special Fred's Final Fling. While getting a check-up, a doctor holds up Fred's x-ray, prompting Flintstone to joke, "How 'bout it, Doc? Flintstone in an x-ray-ted picture!"
