I used to be a huge pickme. Not just romantically, just around everyone. I think it was because anytime I showed interest in something, my parents would tell me how stupid it was. I literally had no interests as a child because of this. My mother is also a huge narcissist who must always have everything her way so I developed into the freeze/fawn type. By copying others or doing what I think they wanted me to be, I was fawning as I was so used to having people turn on me without warning. I was also just desperate for attention and acknowledgement that I existed so wouldn't be the one to break anything off out of fear of being alone.
Radfem groups, FDS, NC with parents/fake friends all helped me.
Probably the biggest turning point though was realizing that people don't respect people without boundaries. It goes against what you might think intuitively, that the kindest, most accepting, easy going person will be the most liked. Instead, people need boundaries and push back or they will just walk all over you then snap at you for given the smallest amount of push back.
You also have to accept that some people are so incredibly narrow minded that they will sneer at anything outside of their own preferences. These people surround themselves with pickmes. It doesn't matter how accepting you are of them, how much you pretend to like the same things are them, or how much you turn a blind eye to their bad behavior, they won't do the same to you. If you say anything outside of what they consider acceptable, you will be bullied, badmouthed, and frozen out just like everyone else. You need to have strong sense of your likes and dislikes and accept that not everyone will think the same and not everyone will respect your opinions.
There's also people who use you to take out their own frustrations, like a human emotional punching bag. If you're a pick me who doesn't give them any push back then they will just keep doing it again and again. They will mock every little thing you do but if you give the smallest push back they will freeze you out until they try to pick you up again later for round 2. With these people you need to train your self to catch bad behavior and stop shrugging it off because they will just get worse.
Overall, the biggest tool you have as an anti-pickme is just getting up and leaving. Don't sit there and take it. Leave and ghost them. Whether they understand or not is not your problem.