I cannot speak for him but my older sister used to bring it up whenever we had any form of disagreement just because she knew that it wouldn’t matter what I had said if she could make me feel bad about how I speak. (Keep in mind that she did this as a child; not an adult). Again, I don’t know the dynamic between your brother and yourself but, like you, I was younger than my sister and she was very domineering over me as a result. She saw it as her responsibility to look after me, regarding other people, but her interpretation of this was to just encourage other people to be mean to me and wait for me to toughen up. She liked feeling like she was “in-charge” of me so she liked making me feel useless (or, at the very least, I always suspected this). My older brother, in between us both in years, was a lot more defensive of me in the manner you would expect and would often scold my sister when my parents were not around. Now we are older, she is not like this anymore because she has her own life. She treats me with ambivalence and mostly only mentions stuff like this when she is trying to encourage me to get married lol. I would speculate that your brother doesn’t have anything better to be doing and treats you like this because it’s the only way to feel like he is still “winning” and it’s also a way to avoid being held accountable by your words. I wouldn’t say some cliché like “oh go and talk candidly with him” because he probably doesn’t want to hear it and the emotional nature of the conversation will probably cause you to stutter and so he will just mention it to kill your case. It is much easier to just accept that even our own family can cruel, even crueler than a stranger for they know only too well how they are hurting you yet feel no desire to stop. Don’t allow his attempts to shame you and shut you down sway you.