Just read this morning that the first time anyone said “masturbation” (not itself a rude word really) on British TV was 1957 - don’t know the context - by Clement Freud, a grandson of Sigmund and perhaps better know in the UK for his dog food commercials with a bloodhound.
In Trials of Rosie O’Neill (1990) Sharon Gless’ character tells her psychiatrist she’s “thinking of getting [her] tits done.” Don’t know if this predates the Designing Women usage.
Monty Python’s Flying Circus almost used it in the early seventies, when Eric Idle, as a man with a speech impediment who pronounces the letter “C” as “B,” declared himself a “silly bunt.”
Designing Women was the first show where I remember someone using the word “bitch” to elicit laughter instead of to show anger.
Two rather surprising (I thought) uses of swear words in recent TV:
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Dr. Green yelling “Shit!” upon finding an unpleasant situation on ER.
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In the pilot of CSI, a new CSI accidentally gets locked in a room with a bunch of dead bodies. Grissom gets her out, and seeing how freaked out she is, lightens the situation a little by yelling “Assholes!” at them. The camera is on the other side of the (closed) door, so the sound is slightly muffled, but it’s perfectly obvious what he’s saying.
It’s interesting to see how swearing is becoming more common on basic cable. Comedy Central’s bleeping of Jon Stewart is pretty inconsistant. And when Jon replayed Robert Novak’s outburst on CNN over and over again, they didn’t bother to bleep it.
Don’t remember what time it was shown, but I remember seeing Scared Straight on Australian telly in the early 80’s. Lots of effin’ and blindin’ in that.
During one of the year on MASH when BJ Hunnicut was on, a wounded soldier called him a “bastard” He thought BJ was letting his(the soldier’s) friend die without treatment so the surgeons could us a leg vein of his to patch up someone else.
Almost forgot, Cpt. Picard used the word “merde” once, muttered softly to himself. Even if it was French it was still a dirty word! 
You must have missed the Weekend Update appearances by the hard-of-hearing Miss Emily Litella (Gilda Radner) on Saturday Night Live in the late '70s. She would editorialize in her little old lady way about subjects like too much violins on television, or presidential erections, until Jane Curtin would correct her. “Oh, that’s different,” Emily would say, and then smile at the camera and apologize, “Never mind!”
Then she would turn to Curtin and snap, “Bitch.”
Designing Women was prime time. SNL was late night.
After what they did to Blazing Saddles, it’s hard to tell what ABC Family won’t edit.
Technically, that first half hour is considered “prime time access.” It formery was used for network programs until the FCC directed it be turned back to the local stations for their own use.
And just to correct my own point, on Sundays, prime time starts one hour earlier.
Also every script had to be vetted by a priest, minister, and rabbi.