The incident, along with many others, is related in this book: Amazon.com: The Real McCain: Why Conservatives Don't Trust Him and Why Independents Shouldn't: Cliff Schecter: Books

There are a lot of articles about McCain's ability to control his temper. "It was early 1992, and the occasion was an informal gathering of a select committee investigating lingering issues about Vietnam War prisoners and those missing in action, most notably whether any American servicemen were still being held by the Vietnamese. It is unclear precisely what issue set off McCain that day. But at some point, he mocked Grassley to his face and used a profanity to describe him. Grassley stood and, according to two participants at the meeting, told McCain, "I don't have to take this. I think you should apologize."

McCain refused and stood to face Grassley. "There was some shouting and shoving between them, but no punches," recalls a spectator, who said that Nebraska Democrat Bob Kerrey helped break up the altercation"

This incident was addressed in an AP article: "There's a lengthy list of similar outbursts through the years: McCain pushing a woman in a wheelchair, trying to get an Arizona Republican aide fired from three different jobs, berating a young GOP activist on the night of his own 1986 Senate election and many more."
McCain's history of hot temper raises concerns - Yahoo! News