Jazmataz, I believe years of experience have taught Dilbert that the PHB does not understand when he is being made fun of, so mocking him in public is quite safe. The punchline can perhaps be interpreted differently, but I think the theme here is that the boss is generalising too much, i.e. trying to solve problems in one field (web development) with 'best practices' from another (carpentry). It is also a good rule not to bite the hand that feeds you if you are a dog. Dilbert just follows up the theme by pointing out he is not a dog. I find it hilarious. ^ ^
I don´t get his finaly answer, that he has direct deposit. What does that have to do with the fact that he´s pissing of his boss and mocking him in public? Does it mean his boss can´t do anything to really punish him for that?