How awful of them, I'm sorry that happened to you. It's been very rare in my adulthood to have people actually laugh, and when they do it's because they had no idea stuttering was even a thing. "I didn't notice" is def the better of the two. Though I've noticed people in customer service or hospitality consistently respond in a way that's actually comforting (since they're trained to). They'll say something like "that is OKAY/that's totally cool/nothing to be sorry about" in the most reassuring tone and it feels both comforting and empowering. I've only had one friend (who belongs to a vulnerable group) ask me what stuttering feels like. I wish it happened more, because it's not an offensive or intrusive question afaik.