Fans wait all year for this one! Credit: Adobe/AllrecipesFew seasonal launches at McDonald’s get fans fired up more than the Shamrock Shake’s return during St. Patrick’s Day. Yes, customers love it when the Holiday Pie and Spicy McNuggets come back, but those menu items are pretty unpredictable in availability.However, if you thought the Shamrock Shake had a cult following, it’s practically nothing compared to another menu item: the McRib. In 20…