"Have you ever had one of those moments when you look up and realize that you're one of those people you see on the train talking to themselves?"

The quote by Marc Maron seems to refer to a moment of self-awareness or self-reflection. It explains a situation where someone understands that they have actually ended up being the kind of person who talks to themselves in public, like those individuals we sometimes see on trains or buses. The quote can be viewed as an amusing way of acknowledging the peculiarities and tricks that all of us have, and a pointer that we are not so various from the odd characters we come across in life. It might likewise recommend a moment of self-questioning, where the speaker questions their own habits and wonders what others may think of them.