When people mock me for it. Or when people claim they stutter because they have a presentation or get stressed. My stutter is genetic and I'm stuck with it for life. I met a grown adult for the first time and my first impression of her was her mocking/bullying how I spoke when I got stuck on my name. I've never cared too much about my name because to me it's just a name, but I stuttered on it and she mocked it. I spent days on end crying over it and I can't really look at her in the same light. I don't know if people who mock your stutter always think you're lying or think it's funny, but it's never okay.