McDonald's is once again featuring some of their beloved advertising characters. Recently we discussed the return of the Hamburglar. But this week, another long-time favorite, Grimace, has been the talk of the internet. The home of the golden arches has been promoting its new Grimace Birthday Meal, which is kind of like a Happy Meal but geared toward adults. In addition to a Big Mac, Chicken McNuggets, and fries, it also features a purple shake...