FanboyFanboy is a derogatory term used to describe someone who is utterly devoted to a hobby or a subject, to the point where it becomes an obsession. Fanboys are often experts on minor details regarding their hobbies, and they take these details extremely seriously. The stereotypical image often associated with Star Trek fans (or Trekkies) can be used to describe a fanboy: a person with little or no social life outside the circle of fanss he or she associates with.
An alternate, more recent example of the fanboy is someone whose enthusiasms are shallow but broad, being directed at a whole art-form, activity, or genre (e.g. science fiction films and television shows) rather than one particular exemplar (e.g. Star Trek). These sorts of fanboys stereotypically show an almost sycophantic devotion to the creators and principals behind a work they are currently entralled by, but will quickly move their attention elsewhere once something better or even only newer comes along. A good example of this is Harry Knowles and his associates at Ain't It Cool News, whose particular focus is on movies in the action, fantasy, adventure and superhero genres.
The female equivalent is sometimes called a fangirl, but they tend to have less of a negative connotation attached.
The letter sequence "FANBOYS" is also a mnemonic for the words for, and, nor, but, or, yet, and so. These words are coordinating conjuctions, which are used to join two independent clauses. It is customary to place a comma after the first clause. Some prescriptive grammarians say that one should not start a sentence with a coordinating conjunction. But others don't. (See English grammar.)