Doctor Stranger Puns

Some man approached my dad and asked him what year he graduated looking at his class ring. My dad tells him class of '92 and he asked how that was possible because my father looks pretty old. He informs him it was for his PhD and that his kids like to call him a doctor that doesn't help anybody. The stranger responds, well my kids call me a doctor that just sits on a stool and passes gas. We were both obviously confused until he let us know he was an anesthesiologist.