My experiences with strangers, even when dealing with shop assistants and such, often used to get me very anxious to the point that I used to try and avoid such situations. So I think I understand where Mongoose is coming from, it's a deep rooted thing. I occasionally do have the odd pang of anxiety now, but it's much less common, since becoming forced into having to face my fears (for example, since learning to drive I've had to pay for fuel for my parent's car; work has forced me to use a telephone and arrange things with people I don't know, etc). There's many a time that I have wished there could be someone with me, a friend who understands me and my inhibitions well to hold my hand along the way through such experiences, but wishing doesn't work, not for me anyway.
When I'm around people I know, I just feel like I can't be comfortable in their company. I get the feeling that I'm boring them, or annoying them even, and that, even though they're being polite and haven't said anything negative to me, that they'd rather hang out with someone more socially adept and interesting. So I end up letting such relationships lapse. I just get the idea that I'm being a burden to people by simply interacting with them. And that's the last thing I'd want to do to anyone.
Also, I do despair sometimes, because I know acquaintances (people that I used to be friends with but have now grown apart from) that are doing all the fun things people do at my age. Like going travelling abroad, something I've never done. There's a nagging voice telling me that if I don't do something about this, when I get into my 30's or 40's I am really going to regret not coming out of my comfort zone.