The Policy
Elitism is, in short, the act of writing or bluntly implying that you are superior to another user. When an elitist act is commited, it can often lead to the withdrawal of a user from the wiki, lack of participation for fear of getting insulted again, or emotional damage on the person behind the keyboard of the attacked. Therefore, these acts should be prevented.
When This Should Be Used
Upon build articles, especially those composed by new users, many people may act elitist. Quite often, when a build is not of a higher quality as another, many people begin to insult it with comments such as "This is so bad", "Absolutely horrible", or "You're really bad at GW. /uninstall pl0x". The purpose of a talk page of a build is to provide constructive criticism, not to flame the creator.
For example:
On Build talk:Rt/A Grasping Spider:
What is so bad about it? Darevil3211 7:21 21 November 2008 (EST)
- The sad thing is you need someone to tell you why it's bad...--
Liger414 talk 16:23, 20 November 2008 (EST)
This is a clear example of elitism, flaming the user while acting arrogant and superior. This is exactly why elitism needs to be eliminated from the wiki, as it can cause harm to the participation of the user and can even go so far as to emotionally damage the human.
When This Should Not Be Used
When elitism is blatently being used as a sense of humor, and the "elitee" consents and jokes along. For example, on User talk:Frosty#Frossssttttyyyy, here is the conversation:
Frosty pwned me at HA last night. :( -- ShazamTheSnake 
hissssssssssss 02:54, 16 November 2008 (EST)
- owned --Frosty
04:23, 16 November 2008 (EST)
Obviously, this can be taken as a form of elitism but generally, one can tell when someone is acting elitist or not.
You also should not use this when someone is pointing out why a build is bad. It is meant to be constructive, and always assume good faith when reading others' posts.
In Short
The act of feeling arrogant and superior is okay, but it crosses the line when it turns into making other people feel inferior. This can cause emotional harm and a fear to participate on PvX. When a conversation looks like it has taken a turn towards flamedom or elitism, place this tag on it.