It's a milkshake from McDonald's. Happy birthday, Grimace. That's pretty. The latest TikTok trend is a little grim. Here's what you need to know. McDonald's limited edition Grimace birthday meal, which includes a mysterious purple colored shake, was introduced in June to celebrate the 52nd birthday of the nostalgic purple character. And of course, as other limited edition food items take the internet by storm, this drink took off with multiple trends from milkshake reviews to people cosplaying as Grimace and painting themselves purple.