Using someone’s insecurity to win an argument is winning with a weapon they handed you in trust.

When someone tells you what they quietly fear about themselves, they are handing you the softest spot they have on the assumption that you will never aim there. Using it mid-argument works, which is the problem. You win the exchange and the trust ends in the same sentence, and there is no way to take the words back out of their head. They will remember that line long after they have forgotten the disagreement.

When you feel that sentence loading, stop talking for a second. Argue about the actual thing, even if you lose.