Not the exact wording but the general premise behind it is a fair counter point in any disagreement. When someone is attempting to gain a higher moral authority, bringing up any hypocrisy is a reasonable thing to do. If pointing out hypocrisy is then dismissed, it is reasonable to assume the other person is not arguing in good faith and therefore should no be taken seriously.
Yes the argument I’m making is about if it is appropriate for the person to be arguing in the first place without considering their own hypocrisy, not whether x is actually bad so I see what you mean about it being off topic. It’s like them saying everyone leaves their shopping cart in the parking lot and it’s bad but when I do it it’s ok, their point about it being ok when they do it is irrelevant, it’s still bad.