Hard to top this (via Crooks & Liars):
Isaac wanted to propose to his girlfriend, so he enlisted over 60 friends to stage a Busby Berkeley street-show lip-dub extravaganza ambush. What follows is five minutes of heart-stoppingly sweet and romantic wedding proposal. I mean: Z. O. M. F.G.
On Wednesday, May 23rd, 2012, I told my girlfriend to meet me at my parent's house for dinner. When she arrived I had stationed my brother to sit her in the back of an open Honda CRV and give her some headphones. He "wanted to play her a song"...
What she got instead was the world's first Live Lip-Dub Proposal.