I accidentally nicked a parked car a few days ago. Wasn't a big nock, but I definitely felt it and I caught their door handle with my wing mirror. I didn't have any pen and paper, but it was also absolutely wild weather, pouring rain and windy so I'm not sure a paper note would have been much use. I waited for around ten minutes for the owner, but they didn't show up. We were parked near a gym and a cinema, so they could have been hours... So I phoned the police and reported the accident, left my details so owner can contact me, and drove off. But I'm still wondering if I should have waited? As now car owner has to go to the bother of phoning police etc to get my details.
YABU - you should have waited longer for the person to show up
YANBU - phoning the police to report the accident was sufficient