A close cousin of attacking the person points out that the person giving advice does not follow it.
Key idea
You too (tu quoque) dismisses an argument or advice because the person who gave it does not act on it themselves.
Why it works
Whether advice is good depends on the reasons for it, not on the adviser's habits. A helmet protects your head in a fall whether or not the person telling you to wear one wore theirs last week. Hypocrisy may be a fair complaint about the person; it is not evidence about the advice.
Worked example: Inconsistent, but right
The dentist tells Sam to floss every night. Sam says: "I saw the dentist eat a whole bag of candy, so I don't need to floss."
- The dentist's reason: flossing prevents cavities.
- The candy is about the dentist's habits, not about flossing.
- The reason still stands.
Answer: Tu quoque.
It is fair to bring up someone's past when the question is about them, for example, whether to trust their plan with the club's money after they spent it on snacks last year.
Common mistake
Treating hypocrisy as a refutation. A smoker who says smoking harms health may be inconsistent, but the evidence about smoking is the same either way. Ask: does the reply answer the reason, or only the person?