I just gotta add my two cents!
You've GOT to return to the playground!
There is always a clique of some sort. The quote that maatmama had in her signature says it best: "Sometimes, I feel discriminated against, but it does not make me angry. It astonishes me. How can any deny themselves the pleasure of my company? It is beyond me." Zora Neale Hurston (BTW, maatmama, Hurston is on my list for ten-books-for-a-desert-island!
Sometimes the clique is based on income, or race, or stay-at-home vs. work-outside-for-filthy-luchre, or "What one does for the money", or age, or homeschoolers vs. private schoolers vs. public schoolers (then it is magnet school vs. regular!), or ethnic background, or maybe it is based on what the blazes I decided to wear that day!
Also, people get lazy and an amazing number of people were somehow never taught the most basic of courtesies: making someone else feel at ease. My mother and father were very big on the old manners thing and I realized one day that all that "fussy" stuff was really just about making sure no one felt uncomfortable. If someone uses ettiquette to intimidate, they are NOT courteous.
And if all the above fails, fall back on the old reliable: "Who cares what YOU think?"