I'll say FOB behind closed doors but wouldn't ever say it to someone's face.

Co-worker is super unprofessional. FOBs accents and all don't bother me. It's more of their attitudes such as entitlement and trying to use everyone and anyone but this is just stereotyping here. I also find FOBs to be super nosy and passive aggressive when it comes to anything remotely competitive. They often tend to not pick up on subtle hints either that they're being annoying or rude.

Are you sure he never tried to subtly hint you were doing something wrong and you didn't pick it up? Was he suggesting something or were you too aggressive? Although none of this justified him calling you a FOB in the workplace.