Don't you see that you are pre-judging them, while making the argument that they should not pre-judge you? You know nothing about them or why they did not invite you into their conversation-- and yet, you've made the assumption that they must be stuck up, called them "people of their type," decided that they must have judged you based on your looks, and said "if that's how they are, why would I want to be friends with them anyway!" YOU are the one judging them! And, if that's your attitude about people you don't know, why SHOULD they want to include you?

The problem seems to be both your insecurity and your lack of understanding of social graces. As someone else already tried to explain to you, when you walk up to people talking and they suddenly get quiet, it means they are having a PRIVATE conversation. They are discussing something personal, that is not meant for a stranger's ears. It is NOT rude for them not to include you in a private conversation. And, if you don't realize that you are interrupting and continue to talk or stand there, that's awkward and will make people uncomfortable. It will probably make them avoid you next time-- not because of your looks or your personality, but because you have a tendency to intrude. It feels invasive and uncomfortable.

The fact that you are having the same problem of not being included at work and at this golfing/church event-- and that you say you've have a hard time making new friends since high school-- suggests that the common denominator is you. Everyone at work, at church, at sporting events, etc. is not stuck up. Everyone who does not want to be your friend is not stuck up. Are there stuck up people out there? Yes. But not wanting to include someone who is intruding and interrupting does not make these people stuck up. Simply "not clicking" with someone you've known at work for a long time also does not make someone stuck up. There are people out there who simply don't mesh-- no harm, no foul. We just aren't going to want to be friends with everyone we meet.

If you don't want to be automatically judged or written off by others, I suggest you not do the same thing to them. Calling them stuck up and "their type" is really rude and offensive, especially when you've just said that they are strangers!

I also disagree with those who recommend that you invite yourself to an outing that others from work are planning. If they say they are going somewhere together, I do NOT recommend saying "okay, great, let's go" or "gee, that sounds like fun, I'll get my coat." That is also rude and intrusive; it's not socially appropriate to invite yourself to something you have not been invited to. That will only turn them off to you even more.

However, I do think it is a good idea to plan something yourself and invite them. That way, you're letting them know you'd like to do something with them, you're planning it, and you're giving them the option to attend (or not). If the problem was that they didn't know you wanted to be included or hang out with them, this should solve that problem. They'll realize you are interested in hanging out with them. If, however, everyone turns down your invitation-- or they show up and it's really awkward-- then you'll realize that you have a bigger problem.