Not too much is known about just exactly what killed Andrew Breitbart, the 43-year-old conservative who played dueling roles as both media entrepreneur and media critic. An Associated Press story on his passing notes that his father-in-law couldn’t “pinpoint what happened.” Breitbart had endured heart problems a year ago.

An armchair diagnosis: Breitbart’s work had taken its toll.

Pull up just about any video on the Web involving Breitbart. There he is, working himself into an intense huff about this instance of liberal smearism or that exemplar of media hypocrisy. There were smiles, yes, and wisecracks — but the jovial digressions were always within a breath of stern and red-faced lecturing on how the media is ruining the United States.

“The only thing I know in the world, quite literally, is media bias,” Breitbart said in a speech upon receiving an award in 2010 from Accuracy in Media, a right-wing media-crit organization.

In that address, at the Conservative Political Action Conference (CPAC), Breitbart showed just how his passion for media policing had pushed aside norms of genteel Beltway behavior. From the podium, he looked into the crowd and said this: “Kate Zernike of the New York Times, are you in the room? Are you in the room? You’re despicable, you’re a despicable human being. . . . You came to CPAC to get your prey,” boomed a charming Breitbart. Polite society’s rules about separating a person from the person’s work apparently didn’t impress Breitbart.

The title of the Kate Zernike story that had incensed Breitbart? “CPAC Speaker Bashes Obama, in Racial Tones.” In the story, Zernike wrote that Jason Mattera, now editor at large at Human Events magazine, had used racial stereotypes and had adopted a “Chris Rock voice” in various rhetorical appeals to his audience at a session at CPAC.

Breitbart then gave his audience a classic hard-soft combo: “She’s the one that correlated his voice to Chris Rock. He happens to be from Brooklyn. He was using his voice. But this is what these creeps do. I’m sick of having cocktails with them. I’m now at war with them. No more cocktails.”

Mattera, in an interview today, says that Breitbart’s insistence on fashioning his own rules served as an “inspiration” to him. And he shares the take on Zernike: “She’s a despicable human being,” says Mattera, arguing that he took his speech and created a “false narrative” around it. “I’m more ethnic than that broad any day.” (Zernike counters that Mattera has never met her and knows “to the best of my knowledge, nothing of my background or heritage.”)

In his CPAC address, Breitbart also attacked reporter Carol Leonnig of The Washington Post, complete with a reenactment of a phone conversation. ”When we basically forced them to acknowledge the [ACORN] story existed, Carol Leonnig [of the Washington Post] called me up and I said to her, I said, ‘I’m interviewing you too because I don’t trust you,’” said Breitbart.

Ad hominem attacks on members of storied media companies — that’s not your Washington establishment school of right-wing media slamming. Broad, angry and impersonal quips are the standbys of this kinder, gentler approach, as executed routinely on the campaign trail by Republican presidential candidate Newt Gingrich. He’s always good for a crowd-pleasing reference to the ills of the “elite media.”

One elite media member denies Breitbart’s allegations. “I can’t remember if I was in the ballroom at CPAC when he said it — I think maybe I had stepped into the hallway when it actually happened,” writes Zernike via e-mail. “But needless to say, I’d disagree with his assertion that I’m the most despicable person alive, or whatever it was he said.”

And Leonnig suggests that the mainstream media serves more than one purpose for a guy like Breitbart: “Like the happy warrior he was, Andrew emphasized what he wanted to emphasize about our conversation to try to show a liberal mainstream media at work. In reporting, you get used to that. Later, his website enjoyed a real heyday with the exclusive reporting that I and my partner Joe Stephens did on the Obama administration’s flawed decisions in funding solar startup Solyndra.” Leonnig also notes: “To his credit, he never declined an interview.”

The Internet bears testament to the guy’s media-friendliness. Though he died far too young, he claimed a lifetime’s share of bandwidth. If there was a camera available, there was Breitbart, taking all questions and free-associating himself into monologue territory. Jeremy Peters of the New York Times reported that he “passes along his personal e-mail address to almost anyone who asks.” His frequent appearances on cable networks plus his Web site properties, featuring Big Government, Big Journalism and Big Hollywood, made him perhaps the most successful member-cum-critic of the mainstream media.

One of Zernike’s own recollections reflects just how quickly Breitbart could change hats: “I had seen him only once before, at the Tea Party convention in Nashville in February 2010, before he was about to take the stage to introduce Sarah Palin. He was hanging around the risers in back where the cameras were set up, with a glass of wine in his hand, joking around with some of the reporters. I didn’t realize who he was. I thought he was just another reporter, then suddenly he was onstage delivering this fiery anti-media speech.”

Pity the obituary writers, who have to sort through Breitbart’s various roles and, in some cases, his contempt for their own media outlets. William McDonald, the obituaries editor of the New York Times, says that “if Breitbart had an ax to grind with the New York Times, which I’m sure he did,” that consideration wouldn’t necessarily figure in the obit coverage “unless it became a news event.” And just what qualifies as a news event these days is anyone’s guess.

Andrew Meacham, a reporter at the Tampa Bay Times who does obituaries, voices the sentiment that many of Breitbart’s targets in the mainstream media must feel: “The conundrum about him, just having seen him on television, is that I can’t figure out if he was really a committed ideologue who was also trying to make a name for himself, or if he was largely having fun by creating this character, and in the course of doing that, sometimes got carried away with himself.”