The term "Shock Jock" is highly subjective and is most often used by narrow minded individuals that feel that there is a boundary too far in media, or even just in humor. There is no line that need be crossed for there is not, and never should be, a line. The whole point of the First Amendment was to ensure the right to say anything, regardless of how controversial or unpopular. "...No bar to the communication system..."
The term "Shock Jock" is usually a throw away line to dismiss anyone that the person is referring to as a "garbage" radio personality or a schlock type comic. It insinuates that the dialogue in question has no validity and therefor has no social merit. Again, extremely subjective and to be taken with a grain of salt.
The FCC Federal Communications Commission (which by its own description is blatantly unconstitutional) has drawn this imaginary line, and has caused just as much damage to the Constitution and the Bill of Rights as the September 11th attacks have caused to individual freedoms. They turned radio personalities speaking their minds into "shock jocks" the same way prohibition turned moonshiners, and even club and bar owners into "bootleggers", and the way the "drug war" formed the cartels and black market dealing we know and love today. The old "freedom with responsibility" excuse they try to use has no bearing on the original intention of the First Amendment and serves only to cause a backlash. The forefathers were well aware of the possible abuses of government and did their best to re-enforce this through the Bill of Rights.
The first person to really be called a "Shock Jock" was radio personality Steve Dahl. Not because he was shocking in the true sense of the word, but because he discussed things that people didn't necessarily discuss in public (sex, marital stress, drugs, just about anything) much less on the radio. He spoke his mind in an unformatted and free flowing manner, unlike anyone on radio before him. The same way as comedian Lenny Bruce or any number of social satirists from Lenny on have done. He broke the foreground for people like Howard Stern and Don Imus. Even the unoriginal Mancow who owes his career to people like Dahl, Stern, Johnathan Brandmeier, Neil Rogers, etc. Their shows were nothing like what they are now until Steve Dahl's show in the late 70's and 80's. Steve Dahl certainly wasn't the first to speak his mind on the radio, but he took it to the level it has yet to surpass.
Dahl was the first to really be hassled by the FCC. Dahl and his former partner Garry Meier, with the cooperation of their station management at the time (Infinity Broadcasting), were the first to refuse to pay the FCC for violation of contemporary societal standards. They ultimately won, proving that the misnomer of "shock jock" is a fallacy and a highly subjective term, and that one person's complaint or an antiquated FCC guideline is not a true reflection of what is contemporary to society. They also proved what Lenny Bruce said all along: "the suppression of the word gives it its 'evil' power." So when you hear the term "shock jock" being bandied about, consider the source, and remember that context is everything.
Then, if you are a fan, thank Steve Dahl for his important contribution to talk radio and free speech in America.