A Trueman moment is a phrase derived from the movie, The Trueman Show with Jim Carey. The directors would explain any random thing that happened so Trueman wouldn’t catch on to the fact he was living entertainment. A Trueman moment is a moment that you experience but there is no rhyme to reason for it. It is just a random moment that cannot be explained.
For example, you could be driving along River Road in Sonoma County out to the coast. You could pass by a fellow on the side of the road. In a normal scenario, you would simply pass by and not think (or look) twice.
However, if this person were dressed in leather pants, leather hat, and a leather vest, you might do a double-take. If this person were standing in an odd position because of the walking stick or cane or whatever he was holding between his legs, you might do a double-take.
The moment that defines this moment as a Trueman moment is the moment you realize that this person is standing on the side of the road, outfitted in leather pants, leather vest, and a leather hat. He is standing awkwardly because he is clutching some sort of stick between his legs. He has slid his leather vest off his shoulders AND he is licking his chest!