This happened last semester of college, so a 3-4 months back. I'm posting now because I only discovered this sub a couple days ago, ok story time. So every Monday Wednesday, and Friday, I had this astronomy class, and the class that was being taught right before my astronomy class was supposed to be finished at 9:50 AM each of those days, with my class starting at 10:00 AM. For countless weeks I'd been walking in a couple minutes after 9:50 and most students from the previous class would be gone or leaving, so I could sit and wait for my class to start. One day, I get to class and when I open the door, the professor from the previous class is still lecturing. I didn't want to look like an idiot, and the door was in the back so I didn't distract anybody when I entered, so I took a seat in the very back. As soon as I sat down, the professor stopped lecturing for a good 5 or so seconds and just gave me this death glare. This prompted everyone in the class to turn around and stare at me too, then he continued lecturing. This made me feel terrible, and I immediately begin questioning whether what I did or not was wrong. I checked my phone and the class was supposed to be over 3 minutes prior, so I wasn't sure whether I was wrong for "interrupting" or the professor was wrong for going late and making a show of my sitting down. Help me out reddit, AITA?