It happens to me, too, and I usually just laugh with them. From what Ive noticed, people initially don’t know that I have a stutter, and just think I tripped on my words. A lot of people without stuttering issues say “I can’t talk today” or “I have a hard time talking today” after they fumble a couple of words. Sometimes I feel like they’re laughing because they think it’s one of those “I can’t talk today” situations. But yeah, I usually laugh and say “yeah, I have a stutter” and it usually ends with an awkward apology from them.