Going to ignore the gaslighting comments above from people who have accepted that they will be treated poorly. NEVER allow anyone to minimize you. We wouldn’t mock someone for something they were born with or can’t help - neither should they. Period. At this stage, it’s important you make it clear that you do not want the stutter to be a spectacle anymore. A stutter is a disability. Maybe writing it in an email will be helpful. If the boss sees you putting it in print, they will realize that it’s not all fun and games and are endangering the workplace in becoming hostile. If you are worried about ruining the dynamic, then it’s just a conversation in person—“hey, I get you may not understand the situation with my stutter, but I don’t want a spectacle to be made of it anymore. I’d appreciate if this was the last time we talked about it or brought it up.”