Mine is when I went to the ocean for the first time and saw how beautiful it really is. I know that sounds kinda stupid but yeah.
Hmmmm, mine's was on new years eve when my great-great grandma (who's only 92 now my great-grandma is 75) started to sing on the karaoke machine "Paper roses" and she pulled me up with her (i was 6) and we danced.
Probably my first kiss with a guy, and all that ensued after. (Suffice to say we went farther than kissing.) It may be a juvenile pick, but it's the honest truth.
Spending a whole day and night romantically with some who completely understood me. He's an ex now, but is still my best friend to this day.