This Isn't Where I Parked My Car!

So, today about 40 minutes into my IO class, some cool cat wearing stunna shades walks in. He opts to take a seat which requires him to walk the length of the classroom between the students and the teacher instead of taking the seat closest to the door. Obviously he's not in our class. He sits down and pulls out a notebook. I don't think he was taking notes. He certainly wasn't taking off his shades. People were trying not to giggle too loud when he sat down. You could see that it affected the professor's composure. The kid left about 5-8 minutes later in the same cool fashion that he entered with. This time it was impossible to keep the laughter inaudible. Seriously...how do you not realize a mistake like that sooner? Oh well, thanks for the entertainment.