The unwritten rule

I am not going to start out by telling you a joke, I will simply tell you what happened and then you can decide whether or not it is humorous.
On March 17th 2009 I walked into class to find another girl in my seat. In college there aren’t assigned seats, as adults professors believe we can find our niche wherever there is an option. I do not believe their logic, in every class I find one seat (after trying out other unsuitable options) and then commit to it. It is mine. It is the one sure thing in my day at school. Other students, abiding by an unwritten rule, acknowledge one another’s choices and tactfully avoid those territories. In the off chance someone defies the status quo and sits where they do not belong, the owner will come into class, see the thief (be irritated but not show it) and find another place to sit without one word ever being spoken.
Upon=0 Acoming into class and seeing this girl, smiling while plugging in her laptop, a dull sort of anger coursed through me. To the left of her my friend, noting my arrival, shrugged her shoulders in regret mouthing, “I’m sorry.” The boy Sam who sits in front of me gave me a what-can-you-do? kind of look. A confusion had taken over at this point as well because, this being a huge lecture class, there were numerous empty seats. Why would this girl pick my seat? In the midst of a group of people she doesn’t know?
I took a step forward (before that I had been standing quite still, just staring with eyes full of clouds) half planning to just sit on the opposite side of my friend, she would have moved her stuff for me. Then another thing occurred to me, my sociology professor had spoken of an experiment where one purposefully sits in another’s seats just to gauge the reaction. The professor claimed that most would be annoyed but never engage in a confrontation. I took another step forward, imagining sitting in that foreign place, no wall to lean on and no Sam to gossip with.
My steps carried me up the aisle and=2 0in front of the girl. She looked up in confusion but I was full of righteousness and I would smite her. “You’re in my seat.” The unplanned words came out with no hint of uncertainty (I never even considered the possibility that I was wrong). “Sorry but I’ve been sitting here since the beginning of the semester and this is just my seat.”
The girl kept looking at me in bewilderment so I went on “I’m sorry but are you friends with Sara (who also looked astonished at my behavior)?” Never during this interaction was my voice cruel; it came out more apologetic and full of compassion for this girl who had made a mistake. “This is-”
“Don’t worry I’ll move.” Her voice was short as she gathered her things then awkwardly sidled around me to find a place for herself further back.
I sat down happily, pulling out my notebook, sticking my bag under the chair and then turning to chat with Sara with my back resting comfortably against the wall. The first words she said were “You’re crazy, I can’t believe you just did that.”
Everyone I’ve told this to has been shocked and told me that I was wrong, rude and/or insane. Their reactions have been bad for my psyche because I’m always certain that I’m right. A lot of my beliefs are being questioned, why was it wrong to take back what belonged to me? Why would the girl have sat there in the first place? Was it a challenge? Are there no unwritten rules? My conclusion is that maybe there is a whole world out there and that a lot of the intense philosophical certainties I have may not be shared by other people.
But this instance was not one of those times, I was right.