I've been reflecting on this a lot recently and have concluded that through a mix of nature and nurture I seem to have developed a particularly sincere/earnest type of character. I am quite a serious person and spend much of my time making sure that what I say can never be misconstrued to be some kind of slight. I am appalled by the idea of offending anyone or saying something silly and am over-polite to the point where I want to scream at myself sometimes for being so bloody earnest! I can make very superficially friendly small-talk but it's forced and practised (and quickly exhausted) and I don't really know how to have a casual joke with someone or build genuine rapport. All of my conversations with the few friends I have are about very factual things - what we've been doing lately, how we feel about serious things that have happened to us in life - there's never any good natured joking or teasing (I'm too petrified I'll accidentally say something that falls flat).
There is a scene in the TV series "Girls" where Marnie's character is assassinated by another and they say something along the lines of "you spend all your energy being so fucking nice and sincere you actually come across as superficial" and I think that's how others think of me. Hilariously for all my efforts I think I come across as cold and inauthentic by others' standards.
I don't see how I can change now. It's such a fully-formed part of my personality. My parents are much the same so I know it's a partly learned behaviour. I find it so difficult to get people to warm to me. I don't know how to build new friendships anymore. The few friends I do have left are ones I made at school where your whole friendship is based on geographical proximity and we still see each other now once very few months, purely out of habit. I'm so frustrated at myself for being so nicey nice and serious all the time but I think it's too late to change.