Andrew Stiles has some good reporting on the feud:

Norquist accuses Coburn of trying to trick colleagues into supporting a tax increase in order to undermine the Republican position in the ongoing debt negotiations. “He’s trying to screw the rest of the Republican party because he is so mad at the world,” Norquist tells NRO. “He didn’t want to get rid of the ethanol tax credit without raising taxes. The important thing in his life was raising taxes.”
In fact, Norquist has been at odds with Coburn ever since the senator voted in support of the Bowles-Simpson deficit commission’s final report, which Norquist describes as “a massive $2 trillion tax hike” and a blatant violation of the ATR pledge. He has constantly criticized Coburn’s involvement in the “Gang of Six” talks, as well as his stated willingness to negotiate when it comes to taxes. Norquist says Coburn’s statements after the vote make it clear that his amendment had nothing to do with ethanol subsidies and everything to do with forcing Republicans to go on record supporting a tax increase — essentially a gateway drug that would inevitably lead to additional increases down the road. “He said, ‘Ha ha, popped your cherry, lost your virginity. Now give me $2 trillion in tax increases,’” Norquist says. “As soon as they voted, he turned around and called them sluts. Guys like that didn’t get second dates in high school.”

Huh. Speaking of getting dates in high school, let us take a look at the young Grover Norquist:

As early as the sixth grade, Norquist, now 47, remembers arguing with classmates over the Vietnam War. "Suzy somebody thought Nixon was a fascist and [Alger] Hiss was a good guy," he says. Thanks to a fire sale at his local public library in Weston, Massachusetts, he picked up several books by J. Edgar Hoover and Whittaker Chambers on the communist threat. At 12, he was volunteering for Richard Nixon's 1968 presidential campaign. After church, his father would buy him and his three younger siblings ice-cream cones and then steal bites, announcing with each chomp, "Oops, income tax. Oops, sales tax."
These are the anecdotes Norquist offers up to explain how his obsession took hold. Politics hit him like puberty, and he has never looked back. "From the moment he gets up to the moment he gets to bed, he thinks, 'How am I going to hurt the other team?'" says Stephen Moore, the president of the anti-tax group, the Club for Growth. "One time I was telling Grover about this woman I met. Most guys would say, 'Oh, is she really good-looking?' or something like that. Grover said, 'Is she good on guns?' He was being totally serious."

I'm guessing Norquist didn't get a lot of second dates in high school, either. Or first dates. (And no, I'm not in a strong position to impugn anybody's high school romantic success, either.)