Sometime in 1994 one of my bosses announced he was getting married. The date set was June 6 and I remember thinking at the time that it was a curious date to choose; D-Day and all that. Nonetheless, marry on that day he did.
The following year, as we stood outside the office smoking and as the anniversary approached I made some comment about how close we were to D-Day. He smote himself on the forehead as one does when reminded of something vital one has forgotten and thanked me for reminding him of his impending anniversary. Thus began a tradition that lasted four or five years; each year as the anniversary approached I'd remind him.
He retired sometime around 1999 and since then it's been up to him to remember - I ain't calling long distance!