When you have enough aviation books that you can find this.
Two different books by two different authors with two pictures by two different photographers at the same airport taking a picture of the same guy inspecting the same plane, taken just seconds apart from each other.
Note, the two pictures were taken at the revealing of the Comet. There were many photographers there, but the fact the two pictures that are so similar are in two different books that I posses is kinda cool.
What are your “you know your an avgeek when” moments?