Fanboy

From Wiki Gonzalez

What is a fanboy?

One definition (inaccurate) is this: "People that are fans of something (the Lakers, Star Trek, anime, Star Wars, the Cardinals, the Macintosh, anal sex) strictly because it is popular."

A more accurate definition is this: "People who are obsessive fans of something (the Lakers, Star Trek, anime, Star Wars, the Cardinals, the Macintosh, anal sex), and relentlessly defend it against all attacks, simply because they are a fan. Criticism of said object of fandom is irrelevant or motivated by jealousy. Requests to get a life or change the subject are irrelevant or motivated by jealousy. Why or how they became a fan of said object of fandom is irrelevant. They make said object of fandom the center of their spiritual lives. Therefore, they inject it into seemingly every conversation, regardless of relevance, and pimp it ad nauseam."

The OED (http://dictionary.oed.com) contains a very early "inferred" baseball-related definition of fanboy under the fan entry:

1919 Decatur (Illinois) Rev. 2 Oct. 6/2 It was a shock to the fan boys when Cincinnati beat the Chicago White Sox.

See, e.g., Cardsfanboy.