I've heard and read this one in various places, in many variations:
a radio DJ gets (disgruntled)/(drunk)/(fired), and as a response (locks)/(barricades) (himself)/(herself) alone in the (studio)/(broadcast station) and plays (the same song over and over)/(as many offensive songs as he/she can find) as an act of rebellion and defiance for several hours.
I am skeptical that such an event could actually occur, since the other radio station employees could kill the power to the station, transmitter or studio with relative ease. One possibility is that the station owner did the deed, considered it harmless and allowed it to occur, or refused to allow the station to go off air. I have read reports of specific anecdotes, but they seem indistinguishable from publicity stunts playing off the popular legend. I would think that a story where there is no punitive action against the DJ is just a staged stunt.
Is there any evidence to indicate a renegade DJ actually managed to lock himself in the station to broadcast material against the will of the station owner for an extended period of time?
Update: From a Snopes discussion board I found, "In 1972, KHJ Los Angeles deejay Robert W. Morgan spun Donny Osmond's "Puppy Love" over and over for 90 continuous minutes, leading LAPD to mistakenly raid the station studios after receiving numerous calls from listeners. The perplexed officers left without making any arrests." The board links to this page. Wikipedia also cites that link. But I can't find any reliable source about that.