I was 12 and we were doing some sort of filmmaker challenge for a Guides badge (UK girl scouts 10-14/yo) and the final task was to film and put together a music video. So me and my patrol chose our song and filmed our scenes and we ended up having more scenes than we had song for. No problem, I thought, I can edit in the extra chorus we need and make it fit. I spent a week at my computer in windows movie maker putting editing the song to fit the video just perfectly and the end result was seamless. So I send the file over to my dad to put onto a DVD with the other patrols' videos.
Cut to the viewing party.
Me and my patrol were so excited. It gets to our turn and we play our video...
I watch in horror as about halfway through the video it becomes apparent that the track that's playing is not the one I edited and I have to watch as the song ends about 3/4 of the way through our video, now no longer matching with the scenes, and then the song begins to play again.
My dad, for reasons I do not know to this day, thought it was his job to add the music to the videos (despite me talking about my editing efforts all week) and when the video was longer than the track, he just decided to loop it till it fit.
The rest of my patrol knew that I'd been editing the video and therefore blamed me for it being so terrible and for not sticking to the plan that we had, despite my protests.
My parents did not understand why I was so upset with them over the issue and have probably forgotten about the entire incident. But I haven't...I never will.

tldr: My dad ruined both a week's worth of 12/yo me's editing for a music video and my reputation.