I like to make fun of the plethora of National *Insert Stupid Thing Here* Days, but as NBC News reports:
Unlike a lot of free-food fad days, National Doughnut Day has a longer, more altruistic back story. During World War I, the Salvation Army sent volunteers to France, where they made doughnuts for soldiers fighting on the front lines. In 1917, the group dubbed the first Friday of June National Doughnut Day to commemorate the volunteers’ goodwill gesture.
Okay, that's kind of awesome.