I'm not, just not. If this characteristic has not yet changed from the age of 16 to the age of nearly 50, it ain't ever going to change. Not proud of it, but... the anti-social response is apparently deeply ingrained.
At 16, I worked at the Azle K-Mart and was sitting alone having hot dogs or something at the store cafeteria on my Saturday lunch break. A girl that I knew vaguely from school also worked there and was sitting with friends across the aisle. She beckoned me over to join them... Now, you would think that any normal person would be grateful for the company and friendly gesture and jump up to join them... I, on the other hand, shook my head "no, thanks." VERY awkward.
At a new job in the early 2000s (in my early 30s), I was sitting by myself at a long table in the work cafeteria. After I was over halfway finished with my meal, a whole group from my department started filing in and seating themselves at the end of the same table. There were still several chairs between us, but there they were, and there I was. A boss spotted me and called me over. Now, being new to the group, you would think that any normal person would be grateful for the invitation and chance to bond with fellow group members... Nah. I, on the other hand, shook my head and said, "I'm nearly done anyway," then scarfed the rest of my food and took off. VERY awkward.
The age-16 K-Mart incident had stayed in my memory all that time, me later cursing myself for acting terribly. Yet when the same type of situation arose 15-or-so years later, I behaved in exactly the same way, despite my awareness of how badly I'd behaved in the first case. I couldn't help myself. I could not bring myself to be civil!
Today at my work cafeteria, it wasn't anyone from MY group that requested to sit with me. But there were outside conference members filling up the cafeteria, and seating was short. I was eating at a table for 4 (where I usually eat by myself), and a 30-ish dyke-y woman plopped down right in front of me and asked to sit down. I said sure. (Already annoyed at a stranger sitting right in front of me; I thought there was an unwritten/common-sensical rule to sit catty-corner/diagonally when strangers are sharing a 4-seat table!) So there we were, eating away, me trying to ignore her. She says, looking at my taco salad: "Vegetables. I ate those yesterday, so I can eat what I want today." I had not being paying ANY attention to what food she had sat down with, but when she brought it up, I looked and saw her two slices of pizza and chocolate desert. Fine. Who cares. I smiled politely and continued munching. She wouldn't quit:
"Are you here with the conference?"
Me: "No, I work here."
"What do you do here?"
"What do you edit?"
At this point I semi-snapped, and glared, "I'm sorry, I'm not trying to be short or rude..."
"Oh! I should leave you alone!"
"I'm not trying to be rude, but I just need to THINK right now."
So for the next few minutes that it took for me to finish my salad, I then had to make an effort to look "contemplative" while doing so.
When I finally stood up to leave, my table-mate said cheerily, "Have a good one!" I did manage a "You, too."
But then I felt horrible afterward. Could I not have made some polite conversation? But I HATE polite conversation. But wouldn't polite conversation have been better than the awkwardness that ensued after my rejection of ANY conversation? I guess not, deep down in my soul.
I left the table feeling like shit for being rude, with a side-psychological-note of "What if she thought I was just rejecting her conversationally because she was so obviously a dyke? I'm gay, too! It was just very weird to me that you sat right in front of me and tried to force me to talk to you!"