They could have felt like laughing but if it was at you it should not be taken personally because in reality they are not laughing at you but at life in general. They could have been stoned and hallucinating and buying tacos to satisfy the munchies and you looked like big bird at the time.
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LOL! I'm new here, and I can relate to that all too well as I used to get upset at stuff like that too. I still do times, but these days I tend to ignore most of them.

They don't know you, so unless they happen to be very immature, they probably weren't laughing at you. Remember, that people who do laugh at other people in public usually want to get a reaction from you. Ignore them and walk away if you can. If you can tell that people are laughing at you, then you can either give them a dirty look or flip them off- LOL!