The couple times it happened in 8th and 9th grade, I just laughed with them while i said "haha thats funny". Kinda kills the whole thing and what they are trying to do to you. Then stop talking to them As an adult it rarely happens but if it does or the laugh, i just give them a look and continue talking. Doesn't bother me, some people never met a stutterer and don't know how to respond.