There are cliques here. And people have in the past made this site unwelcoming for others; either due to group exclusivity behavior, or individually on their own. These are objectively true statements that can be proven with direct evidence.
The forum itself, comprises a group of people. Within that: established members and newcomers form two groups (then perhaps long-time-members, long-long-time-members, what-have-you). Within that: two or more people who are all in familiar, personal correspondence with each other, form a group. And within all of the former, any behavior, coming from/shared by a group, that is exclusive, constitutes a clique.
(I was just thinking, do not men/women/etc.. constitute groups as well? I've decided, objectively not. These are characteristics that, when observed, can constitute a group, conceptually; but, they don't make for actual social groups. Groups based on characteristics only make for, 'conceptual,' groups; ie: people who have blue eyes, people who are tall, etc... So, these, are not groups, for the purposes laid out here.)
Aside from cliquish behavior, there is also hostile, offensive, or rude behavior. This can come from new members, established members, individuals, or groups; ie: anyone.
Hostile behavior is generally easy to objectively define; though the reasons behind it, may differ, as per personal opinion.
Offensive behavior is generally subjective, though, there is often a particularly strong group consensus on certain issues.
Rude behavior, I would say, is mostly objectively defined; in that, 'politeness,' is a defined and shared cultural and social construct; ie: every language that I'm aware of, seems to have words for expressing, 'gratitude,' 'sympathies,' and so forth.
When one is a part of a group, and has a familiarity with one or more people, there is less of a need for, 'formality,' because the participating members have a certain understanding between them, as pertains to the particulars or views, opinions, temperament, etc; ie: you are less likely to be offended by a friend through a social misunderstanding, than if you were to engage with a, 'new comer,' without a more formal and polite approach. For example, I may say to a close friend, 'what's up dirt bag!' and my friend may understand this as a joke, perhaps alluding to a previous conversation. Whereas, if I approached a new comer, with that same sense of lack of formality (based on kinship), my words would likely be construed as highly offensive.
So, rude behavior, I think, is the easiest to spot, objectively. It's also easiest to avoid. One only needs to behave politely.
Offensive behavior is the tricky one, because it's very subjective. And it's complex, because it is often what leads to hostile behavior, or stems from rude behavior.
Hostile behavior is also easy to spot; but, the cause of it, is again, often elusive. It could be due to a misunderstanding of perceived hostile behavior. It could be due to an argument. etc.. etc..
The older a group is, I think, the more often, exclusivity is to be present. This isn't always the case, however.
So, as the devil's advocate, it would seem, by definition, it's next to impossible not to have cliques, on a forum. A group may also prefer to be exclusive as well; and retains the right to do so. Two or more people may simply prefer eachother's company to that of anyone else. About the only way one can avoid being in, or forming a clique, is by maintaining constant vigilance against behaviors that lend themselves to group exclusivity; ie: inside jokes, shared experience within the confines of the group, shared opinions/beliefs/things of that nature, etc.., are all experiences that can influence the behavior of group members.
However, two or more people can be exclusive and judicious in who they allow or don't allow, 'into the fold,' without, generally, being rude, offensive, or hostile. Mistakes will be made, and certain situations unavoidable; but, on the whole, it's doable.
So, there you have it...
