As is quite apparent, the Taiki definition is very negative which may be reflective of Taiki's experiences. I cannot in all good conscience accept the Taiki definition as being reflective of fangirls in general. Almost all of the fangirls that I deal with are older than this and are definitely not as shallow as the Taiki definition suggests. This parallels sharply with the idea of a fanboy, which brings forth images of males with no lives, poor cleanliness and an inability to discuss a series intelligently. It is difficult to explain why the term fangirl has a better connotation than that of fanboy.
Females are proud to be fangirls, but males are ashamed to be considered fanboys.
My best guess to explain this difference between the sexes is that the terms originated at different time periods. The term fangirl I believe became prevalent during the late 1990s. Another reason that I believe to be plausible is that the term fangirl originated from fangirls themselves. This would be contrary to the term fanboy which was disdainfully applied by others to the fanboys themselves. The distinction in connotation would be obvious then.