The phenomenon that occurs when you realize you've been conflating two or more different actors or actresses as a single person. Most common with young actors before they make it big or character actors.
Common examples:
Shia Labeouf and Topher Grace
Kurt Russell and Patrick Swayze Rachel Bilson and Mila Kunis
Omar Epps and Mekhi Phifer and Sean Patrick Thomas
I had serious diactorism this morning when I realizedShia Labeouf wasn't on That 70s Show. Turns out Topher Grace is a different guy.
That mental note sign you put on something to denote its not well understood and likely to fail at some point. You promptly forget about it and years later a resultant disaster occurs.
the designer had second thoughts about the usefulness of the alarm and made a mental note disasterisk to re-think it. Years later the alarm was ignored and the reactor subsequently blew up.