I really like to tell the story of the four colors theorem. I did it multiple times, with various durations (from 5 min to 1h30) and publics (students, researchers, "amateurs"). I was mostly using a board, so no traces remain, but one on those instances was filmed as part of the 5 minutes Lebesgue.
Various traces of science dissemination actions around mathematics and/or computer science I took part in. They are mostly in French, though.