My PI is publicly humiliating me: Why would a PI do this and what can I do to mitigate the damage from this?
The best way to mitigate the effects of his behavior is to be really, really clear on what's happening and stop making excuses for him. This will help you separate out blaming yourself for something you have no control over: his bad behavior. It's your best chance at preserving your mental health while you have to work with him.
This behavior you describe from him is toxic, and it is very likely intentional. He has demonstrated that he has the self control to not make you uncomfortable in one-on-one interactions. He chooses to make you uncomfortable in front of an audience.
Also, teasing in any context, but especially in professional situations, isn't fun anymore when the target repeatedly shows discomfort. Teasing is only acceptable at work when all parties are benefitting from the relaxed atmosphere.
Finally, his sensitive/negative reaction to you asking him to stop has the following effect: it creates as much friction as possible so that you won't keep complaining and will allow him to continue enjoying making you uncomfortable and embarrassing you.
He is an adult and should be able to handle hearing, &quot;hey, this was all in good fun at first, but I'm not having fun anymore, and I'd like you to stop.&quot; A person managing a lab should have the capacity to listen to that. If he can't handle that conversation, he is the problem, not you, OP.
Also, I would try to avoid speculating about why he's like this or what's going on in his head. It's getting you more wrapped up and emotionally invested in keeping the peace with him, which will make it more painful when he decides to be cruel. Try to decouple from his thoughts/emotions, and just focus on behavior. His behavior is unacceptable. You've asked him to stop, he refuses. That means he's wrong to be saying these things to you. Try to keep that in mind, and hopefully it will help you stay less stressed out and not internalize the negative and inappropriate things he's saying.
ETA: Upon rereading your question, it looks like you may not have directly asked him to stop teasing, but that you know him well enough to know it will go badly. You have the higher moral high ground if you directly ask him to stop, and I would try it once, but you know him best. If he's created an environment where you are sure speaking up will just cause more difficulty, he's still the problem and my advice stands.