Erik May is the president of Flags Unlimited, and usually sells US, state, and military flags.Nic Antaya for BIA flag business in Michigan has seen a boom thanks to the World Cup.Usually, Flags Unlimited mostly sells US, state, and military flags.But the company's president, Erik May, said he was blindsided by increased demand for foreign flags.This as-told-to essay is based on a conversation with Erik May, 43, who is the president of Flags Unli…