A clique, at heart, is just a group of players that spends most of their time on one another. It's those five friends who make related concepts and RP with each other all the time in their corner. They aren't necessarily hurting anyone else, but they're not helping anyone else, either.
Those people are fine. No one is obligated to play with others, nor is exclusion a sin. If you want to play with Bob, Jimmy, Jackson and Eugenia, everyone else be damned, go wild. It's your time and your fun.
Now, the staff-facilitated cheapness and cheating @Ghost mentions, that is an issue.