Well, you won’t be arrested by the New York Mets Turn Those Thumbs Around Shirt. If you mean actual rubber or plastic flip-flops maybe wear some nice leather sandals or slides instead if you are really intent on wearing an open shoe. If you are visiting you are likely to walk and take the métro a lot, and I’m not sure sandals are the best choice, but you said somewhere else that you can’t stand shoes, so it’s up to you. That said, fashion rules are made to be broken. If you can make flip-flops work in a stylish outfit, then bravo!