Mine was with a coworker, We had been friends for years, but something had changed between us in recent months. We met for a pint after work to talk.
We discussed all the practicalities of why we couldn't be together, my dcs and the fact that I was moving away, the fact he wanted dcs, and I didn't want anymore etc etc: All the things to do with why us being a couple was a bad idea.
So having had this sensible, frank, grown up discussion, we decided that we'd stay friends and not pursue anything more.
We finished our drinks, walked out to the car park (where it was dark and drizzly), and I kissed him goodbye on the cheek, saying I'd see him tomorrow at work.
It was sad. He was gorgeous and lovely and kind. We had so much in common, but it just seemed the odds were stacked against us.
I turned to walk to my car, and as I did he caught my hand, spun me back to him, saying, "I can't just let you walk away" and kissed me.
The rain started pouring down. And there we were, stood in a carpark (without coats) snogging the faces off each other 
I swear everything slowed down.
Now we're happily married. Have just had a baby together. And could not be happier. He left his job and moved to be with me and the dcs.
That kiss goes down as the most romantic thing that's ever happened to me. A snog in the rain in a carpark after work. Who knew?