MillionMonkeys - Is a standard "I take offense to the last one" punchline.
These guys on TVTropes explain it better than I could (be warned through: if you start clicking on links there it gets addictive)
http://tvtropes.org/pmwiki/pmwiki.php/Main/ITakeOffenseToThatLastOne
I don't believe your assessment is correct. The fact that he is an idiot led him to the conclusion that he was being accused of not traveling on business much.
So the interviewee assumes he's not an idiot, and therefore PHB must be accusing him of not having traveled. I actually don't get the humor (doh!), but is my assessment of interviewee correct?
And would it be better/funnier if he said "How dare you accuse me of being an idiot!"?