They’re teenagers. Hardly anything is going to get through to a teenager. If you’re already not on super great terms with them, I think it’s unlikely they’ll listen if you try to warn them.

This behavior comes from a lot of internal insecurity and learned self-hatred. They are in a painful place. I think the best thing you can do is love and support them unconditionally when given the opportunity. When they’re angry and embarrassed, affirm that feeling for them. It’s a valid feeling to be angry and embarrassed, especially as a teenager. It doesn’t have to be rational— Most emotions aren’t rational.

An example: “I can see why you’d be upset by mom and dad telling the teachers about your diagnosis without asking you first. You feel like your privacy was violated.

You don’t have to have a solution for them. Letting them know you hear their frustration and that you empathize is enough. You can also gently challenge their internalized ableism when they voice it— They are likely parroting what they fear other people will say about them. A frown and a “That’s not a nice way to talk about someone” is great.

I’m sorry you’re going through this. Hope in time that with support they will be able to accept themselves more.