Panel 1: We're at John's office today. He's whining to Jean about how awful it is that he, as a dentist, is thought of as running a modern-day torture chamber and is hated for it.
Panel 2: He goes on to moan about how it's extra unfair that a Nice Guy[tm] like him is tagged with such a bad image.
Panel 3: She tells him he could have become somthing else. He could have become a lawyer, for instance.
Panel 4: He rejects that out of hand because lawyers are all crooks. The notion that he's doing the same thing to them that people are doing to him is something he'll make a point of not realizing. If there's anything
Hypothesis: I was sort of right. John's main complaint is that nobody likes him and he's too thin-skinned to realize that doesn't really matter.