Unless he's a real jerk (which is possible), he probably wasn't laughing at you. It's possible that he was confused or nervous and just laughed as a reaction, or it's possible he just thought you were having a bad day, which honestly can be a little funny sometimes. Not in a mocking sort of way, but almost in a solidarity sort of way, like "it's one of those days". There's also the possibility that they're thinking right now "I can't believe I laughed at them, I feel like such a jerk". In my experience, most people don't really care as much as you think. I have a very close friend who I met about 15 years ago, and the first few months I knew him I actually pretty strongly disliked him. I would stutter on words and he would laugh and make a comment about it. I remember one time I stuttered on "people" and he said I sounded like a bird going "peep, peep, peep", and it made me feel awful. But then one day I realized he would say these things and then ask if I want to hang out after school in the next sentence. It dawned on me that he never actually cared or judged me, he just simply thought it was funny in the same way it's funny if you stub your toe or trip on a rock.