Chain: McDonald's
Introduced: 1970

McDonald's is king of the limited-edition menu. They work the country into a frenzy over items that appear once or a few times a year. The Shamrock Shake comes out to tempt patrons in March, for St. Patrick's Day. What does a Shamrock Shake taste like? No one knows. It's not really mint, but it's far more than vanilla. What secrets are contained within the green dye that paints the treat? Presumably the dessert's former mascot, Uncle O'Grimacey, knows, but McDonald's gave him the boot during the '80s, and he took the secret to his Irish cartoon grave.

Mix it with Baileys for a gut-blasting time.