Hey, we see it all the time, dumb people laugh at other people because they lack the ability to see the other person as a living, breathing, caring person with actual feelings. They laugh at transgenders, they laugh at very short people, they laugh and stare at very tall people, they laugh at someone with a limp, bad scar, someone that doesn't fit their criteria, whatever that would be.
Best thing to do, like others have suggested, is to hold your composure, try to hold on to any self-confidence and self-assurance that you can muster and IGNORE the ignoramus. Having a friend with you really helps so until you can again gain your self-confidence it might be best to stick with another person in the short term. It is too bad that this happens but we can only control our feelings and actions and can not regulate how someone else acts... particularly so with the dimwits that try to shame and laugh about others. In time, karma will have it's revenge with these idiots.
As StacyRenee stated in the previous reply, "They're strangers that I'll probably never see again."