Billy Bob is currently on tour with his band, the Boxmasters (who knew?), opening up for Willie Nelson. Apparently when he's promoting his music, he doesn't like to talk about his acting career, as that's what set him off in this interview.
I've always liked Billy Bob - he's strange and plays interesting characters. I know it's his job to promote and give interviews and it was relatively unwarranted for him to give this guy the cold shoulder, I think it's humanizing.
He was in a bad mood, sure. It's no excuse, but who in the world hasn't done the same?
If you follow the link above (or here it is again) there is a video of the incident.