The suddenness of your tears!
David Pogue, a tech writer for the New York Times, put together a marriage proposal that puts all others to shame. Pogue made a trailer of his relationship with his now soon-to-be-wife Nicky, and convinced a resort theater to play it as part of a movie night. A hidden camera captured every moment of Nicky's reaction.
It doesn't get any cuter than this -- Dan sets the scene:
I am a traveling salesman, and I would always take pictures of my self jumping by my Toyota (like the old Toyota commercials). I would set up my tripod and camera and take these pictures alone. Then I started dating Robin and we started taking our own "freeze frames" (as we called them) where we would drive to random places and set the camera and timer up and do silly things. I decided that on my birthday (July 8th of this year), I was going to propose, and record video instead of take a photo. Needless to say it caught her by surprise.