Tropical Smoothie’s National Flip-Flop Day 6/21 From 2-7pm by Dana Zeliff on June 13, 20132013-06-13in Restaurant Deals Disclosure: This post may contain an affiliate link. Tropical Smoothie’s National Flip-Flop Day is back! Receive a FREE SMOOTHIE on June 21st, from 2pm – 7pm, by wearing your flip flops to one of their locations. I highly recommend getting in line just before 2pm! It gets busy – FAST!