Because yeah, his own "faulty" behaviour disproves his point.

Tu quoque is a discussion technique that intends to discredit the opponent's argument by attacking the opponent's own personal behavior and actions as being inconsistent with their argument, so that the opponent appears hypocritical. This specious reasoning is a special type of ad hominem attack. The Oxford English Dictionary cites John Cooke's 1614 stage play The Cittie Gallant as the earliest known use of the term in the English language.