There are four hundred thousand words in the English language, and there are seven of them you can’t say on television. What a ratio that is: 399,993 to 7. They must really be bad; they’d have to be outrageous to be separated from a group that large! “All of you over here. You seven? BAD WORDS.” That’s what they told us they were, remember? “That’s a bad word!” No bad words; bad thoughts, bad intentions … and words.
You know the seven, don’t you, that you can’t say on television? Shit, piss, fuck, cunt, cocksucker, motherfucker, and tits. Those are the heavy seven. Those are the ones that will infect your soul, curve your spine, and keep the country from winning the war.

George Carlin (1937-2008) American comedian

Show (1972-05-27), Class Clown, Santa Monica Civic Auditorium, Santa Monica, California

(Source (Audio))

Carlin's famous "Seven Words" sketch -- which led to his arrest at some venues where he performed it.