The girl sits next to me always leaves on time.

So everyday I wrap up my work and get ready to leave when I see her leaving without even look at the clock. One day she left an hour early, so did I. As I walked out passing by everyone's cubicles, I was thinking how come everybody stayed late today.
I realized what time it was when I got in the car, and I understood why my manager kinda looked at me weired when I walked out.