The first instance of "shit" on American network television (ie not HBO etc) that I can recall was on Chicago Hope. I think it was Adam Arkin who was able to say "shit happens" in one episode. There was a bit of publicity about it at the time.

Chicago Hope also managed to show a female breast, sort of. There was an episode where a woman had one of her breasts reconstructed, and they showed the result. I assume it wasn't an actual breast that was aired, but a lifelike replica. Either that, or they got away with showing a real boob by pretending it was a fake one in the story.