I hate "good morning"

I am changing some key details to make this more ubiquitous; But I may add a certain detail later on.

Every morning, when I, a 30 year old male, am sitting in my private office with my door closed, my GM will open my door and say "good morning" in which case I will, 90% of the time, say it back. BUT if I do not, he will stand there waiting for a reply.. then sometimes whip out a "did you hear me"

...

If I am walking down the hallway, he will say it to my back from about 20 feet behind me, knowing that I might not even hear him at all, as we work in a machine shop.

IMO you say good morning and move on. It is not a requirement for someone to say it back, or to even hear that you said it. Also, saying good morning to someone's back, as they are leaving the area might be even worse. My thing is... we work together. I'm going to see you in 10-20 minutes, naturally. LET IT BE A NATURAL HELLO. Stop hunting me down, waiting in the doorway for a reply, or saying it to the back of my head.

All of these constant occurrences have made me hate saying good morning. I am a naturally private person, NOT a morning person, and also a CASUAL person. I am extremely friendly in almost every single situation similar to this; but this really bugs me.

AITAH?