I know this is WAY advance warning on this one, but I like to post these things so I don't forget them, and then remind you when it's closer to the actual day. The latest bogus promotional pseudo-holiday is "National Flip Flop Day," which is June 19, and on that day you can get a free 24 oz. smoothie from the Tropical Smoothie Cafe when you enter the store wearing flip-flops.
No locations in Washington, boo, but you can check this map and see if you're one of the lucky states that can enjoy a free smoothie in about a month.
You can also sign up for their email club and get a free smoothie on your birthday, so really, there's no reason you should have to pay for a smoothie ever again.