My mom has done this with me a lot, I've been adamant all of the way and if I wasn't she just never would've supported me. I know she loves me but also it's weird that sometimes she tries to deeply validate me and sometimes she just insults what I want to do.
Likely a personality disorder though, my mom herself is not very mentally stable but I wouldn't change her for any other mom.
It took me a while, and that mean boy did not disappear, but I've made improvements towards being a better person. What I did was mind my manners and habits continuously throughout the years, I believe there is no other way.