The cashier made inappropriate remarks. That's about him. For whatever reason, and it could also be social anxiety, he doesn't know how to connect with people in a positive way.

When you can see that others' remarks only speak about them, you won't have the mistaken belief that their remarks are about you. It takes practice and reminders to yourself, but eventually their words will lose any zing and hurtfulness. Next time you might even laugh at the absurdity of his idea that he can control/dictate what other's wear. Talk about delusional!