Cliques should've ended in high school

In high school I learned that certain people are drawn to particular groups of people. It's not possible for everyone to be best friends with everyone else. Certain interests, activities, behaviors set people apart from one another. Going to a small school, however, I saw that these groups could peacefully coexist and interact with one another. Most of the time I felt perfectly comfortable approaching people who I didn't speak to on a daily basis.

In college I couldn't be bothered with cliques. I talked to everyone that I wanted to.

My department is very team-centric. It has to be. Little tedious tasks - gathering information, making calls, preparing supplies, etc. - are dealt with so much easier when they are shared by several people. We all interact with each other at the events themselves too. So it really surprised me to realize that I would have to deal with cliques at the workplace.

About 5 people who are in their early 20s started this summer. 4 of the 5 just graduated from college. 4 of the 5 are female. Naturally a person would group us together. That person would be wrong.

It's not that we don't get along, but I don't understand exclusivity. I've never been in an environment where I had to deal with that. I was always welcome. Now all of a sudden I'm not. I'm excluded from after-work debauchery. I'm excluded from weekend fun. Now don't get me wrong, it's only been several times, but that doesn't make it any less annoying.