This is so interesting.
When I think about myself, I'm always polite, but I'm very quiet and introverted, so in the brief amount of time it takes to check in, I wouldn't make an impression.
Although I've never been upgraded, I have frequently been given seats with vacant seats beside me. That even happened on the packed out flight home. It allowed me to stretch out and sleep.
Of course, that could be because I'm so repulsive, they don't want to put anyone beside me....lol