The ice cream treat debuted in 1970, and since then, McDonald's says the shamrock shake has stirred up a "cult-like" following who crave its icy goodness when the St. Patrick's Day season is nigh.
What you might not know is that it had its own mascot back in the day, named Uncle O'Grimacey, who of course, spoke like a stereotypical green Irish monster and extolled the virtues of all things green, including the shake.
The Bacon milkshake is supposedly a secret item so you'll have to whisper it under your breath as you order it. According to the Jack in the Box a regular bacon shake has 773 calories and 40 grams of fat. Tasty!