I sometimes get told when people react or even giggle when I stutter that they are either reacting to getting caught off guard, think that I'm trying to be funny, or don't know its an issue and they didn't mean to make fun of me. But if someone knows ahead of time, I would like to think that they have time to prepare themselves to NOT react. Especially laugh. So, if it were me, I would immediately be turned off and uneasy about speaking with them. But that's just me. I take it very personally if someone knows, and they still laugh.