I was about to propose to my girlfriend and was setting up my DSLR on a tripod to take photos via IR remote (she thought we were just going to take photos of us at sunset).

Then a guy came walking by and offered to take the photos for us. I demurred, but he said he had the exact same camera and knew how to use it. So I quietly told him what was about to go down, and he took a bunch of great photos of our engagement.

For at least a year after, my wife didn't believe that he wasn't a plant!