How would you feel if a close friend of your partner trash talks about your appearance to them and your partner considers what they said?

The “friend” should keep their opinion to themself. Not only is that rude to you, but also a shitty way to treat someone they are supposed to care about. It’s one thing to approach the topic in a concerned and caring way, but another entirely to trash talk the other person. Also, if my SO were to allow someone else to not only talk about me like that, but also to consider what they said as valuable input, then they can find a new SO.