Depends on who it is. If it’s a friend, I don’t make it a big deal and just say to don’t do that. If it’s a colleague, I say that’s unprofessional and inappropriate. If it’s a stranger, I go on my way and wish that they unlearn stupidity. I had a boss that said, “If I had a stutter, and someone were to make fun of me, I’d beat them up.” Now, I’m not a violent person, but it gave me the realization that I shouldn’t have to be embarrassed by my stutter.