As a stutterer, this has happened to me several times. However, I've realized that people might laugh/get mad/ignore if they don't know how to react to someone stuttering. Usually they don't do it out of malice, but lack of awareness. If someone laughs at me, I inform them that I've a stutter, and that it's not nice to laugh at someone's stutter. 99% of times, they apologize. If they continue to laugh, then I know I'm dealing with a piece of @#$%, and that they'll laugh at me no matter what.