You know, I had been making distinctions in my mind of fangirl and fanboy behaviour as applied to something completely different ;) football yeah. Neither being that desirable in my mind, though I find myself having traits of both of those ( as defined by me). I have not been on enough fandoms to really understand the dynamics ( plus honestly, if I love some characters I do not want other people´s versions of characters, in writing or visually messing my concept of them) I am just an observer , but have you considered the crucial in defining fangirl and fanboy might be not the gender thing difference but the girl/boy implying teenage? The most extreme types of fanboys and fangirls to my mind sound like teenagers ( or teenagers in maturity levels). Though sabotaging that theory I can think of setups with older fans formed mostly of one gender where it sort of fits those stereotypes :(