I agree that every congregation has cliques because that is simple human nature. As someone else has said, we tend to gravitate toward people with whom we share interests. However, it is one thing to have friends in the congregation, it is quite another to deliberately shut others out. One problem I see in this regard is the great divide that exists between married people and singles. When I lived in the Deep South, that divide was especially pronounced. In many congregations, married couples couldn't tolerate single people, and went out of their way to either exclude them from gatherings and other association or, even worse, tried to "fix them up" with someone in the hopes the couple would eventually marry.
The WTS doesn't help matters with its distorted view of what family life should be and how singleness is to be enjoyed. For the WTS, single people are cannon fodder to be employed in the full time preaching work or serving in the various Bethel outlets around the world. I am still single, and I remember dreading the talks, meeting parts, book studies, and other things that focused on "family life". District conventions and circuit assemblies were the worst for this.
When I moved to Colorado, I noticed that married people were more tolerant of singles than the Witnesses I knew in Alabama had been. Still, they tended to associate among themselves more, and single people were often left out. While I never felt hated, I didn't entirely feel wanted, either. I learned that if I were to enjoy my life, I was going to have to be proactive about seeking that joy. The congregation had very limited resources in that respect.