Best thing that happened to you or the best thing you did, whatever. You proposed, you graduated, you avenged your father's death, etc.
I had a lot of great moments this past decade. Setting aside those that took place in my dreams or waking fancies, I'm left with maybe one really great moment: that one day back in high school, which I believe I've referenced all too often here, when I interrupted a class to sing to a girl I liked when she felt down. Seems like that single moment inspired all the good things of my high school experience that followed. Not a single thing I've done since has been so genuine, wholesome, and spontaneous.
Kinda sad, I know. So! How about you.