I think soft YTA. You don't need to come in hot with, "is my speech impediment funny to you?" It's pretty normal to laugh and poke fun when people fuck up words. It happens to everyone, and no one means anything by it. I'd understand getting pissed off if its someone who already knows you and about your stutter. But it's a strong reaction to someone trying to joke around with someone they've just met. Just say "i have a stutter, by the way." No need to make it hostile