A few days before taking my girl to a musical at Esplenade, I secretly dropped by the place on my own and picked up one of those folded glossy leaflets they always use to introduce the troupe and market the show. I scanned it all in and modified it so it contained my proposal in pretty bold text. The modification had precisely the same look and feel, same font, same colors, it blended right in with the leaflet. Actually quite easy to do with today's software.
Had the whole thing printed on the same kind of glossy paper and folded it the same way as the original. I kept it hidden on me while watching the musical with my girl later that week.
After the performance had ended, we walked by the Esplenade lobby on the way to the exit, at which point I casually said we should pick up a musical leaflet from the counter. A few minutes later, after reaching the car, I put the leaflet into my coat pocket.
So of course, while taking her home, we're still chatting about the show, how fun it was etc. When we reached her apartment, after we'd got out of the car, I mentioned one the musical character's outrageous red outfit that I knew actually wore a yellow outfit. She took the bait and after a minute or so asked me for the leaflet that we'd picked up earlier so she could use it to prove me wrong. Of course, I slipped her the modified leaflet instead.
Well, the look on her face when her eyes caught my inserted text was utterly priceless. She must have taken half a dozen double-takes between me and the leaflet, speechless all the while. When I went down on one knee, she lost it.
Anyway, she accepted, so yay.
Not majorly massive to set up, yet it packed plenty punch and was very rewarding eh.