What do you say when a person (unknowingly) laughs at you...

What do you say when a person (unknowingly) laughs at you... Quite a few times, I've been in a social situation where I will stutter and someone who doesn't know I stutter will laugh and say something like "haha are you okay there?" or mimic me, anything along those lines. They usually feel terrible after finding out I actually stutter and it wasn't just a one off. I like to throw around a bit of banter, I can take the mickey as well as give it. So basically I'm looking for something witty to say in these situations. Ty for any suggestions!