I feel left out a lot. It is particularly hard for me at work. We have 8 women who work together, and (with the exception of one girl), we all get along very well. I find it annoying (both personally and professionally) when there are 3 or more of us working together and the other two are chatting while I work. I have found myself butting into conversations and following people around like a lost puppy trying to be involved, which I think makes me look pathetic.
I also often hear about friends going out without me, but it doesn't always bother me, because odds are, they are doing something I don't necessarily want to do. Besides, if it's only a couple of people, I don't feel too bad, since there are times I go out with another person and not include others.
In high school, one of my exes made a diagram of all the cliques in our school. He described me as a "floater", meaning that I didn't affiliate with one particular group, but could fit in anywhere. The flexibility could be a good thing, but I also missed out on a lot of inside jokes and group activities. I have come to realize (since I still hang out with 2 friends from high school who hung out with different groups in h.s.) how much I have actually missed, and it makes me sad.
Sorry...that was a lot longer than I intended...and I could write more...