As a point about logic, that is a description of a bad argument. As a tactic it is a description of where your attention goes: the attack is the bait, and defending yourself is the trap.
Why it is hard to leave alone
Recognising a personal attack is rarely the hard part. Leaving it unanswered is, because being publicly mischaracterised creates a pull toward correcting the record — and correcting the record means talking about yourself.
That is the mechanism this site is describing. Once you are explaining that you are not lazy, not paid, not stupid, not lying, the original subject has been dropped by mutual consent.
What it looks like
- The reply addresses your motives, competence or history rather than your point
- A specific accusation you feel obliged to deny, especially a near-miss one
- Something about you that is public and slightly embarrassing, raised as if relevant
- Praise-shaped versions: "I'd expect better from someone as smart as you"
- The escalation is personal while the topic stays untouched
The honest difficulty
Not every remark about a person is a fallacy, and treating it that way is its own error.
If someone is advocating a policy they will personally profit from, saying so is relevant. If a claim rests on someone's firsthand account, whether they were present matters. If a person has been wrong about the same thing repeatedly, that bears on how much weight to give them now.
The test is whether the point about the person is being offered as a reason the argument fails, or as information about how much to trust an unverifiable claim. The first is a fallacy. The second is ordinary judgement.
What to do
Do not defend yourself in the thread. This is the difficult part, because the urge is strong and the accusation may be plainly unfair. But a denial is a paragraph about you, which is the subject the attack proposed.
Restate the point once, without reference to yourself. "The claim was that X. That's still the claim." It is short, it does not engage the attack, and it puts the subject back in front of anyone reading.
Leave the attack to the room. Answering it puts the accusation into your own words as well as theirs, and gives the thread a second reason to keep discussing you rather than the subject.