The term "fanboy" is derogatory. In every instance in which it's used it's intended as an insult, a criticism, and/or to dismiss or diminish the target's opinions or position. Given that it's used on fansites and sci-fi/superhero/fantasy discussion forums, it seems to mean "a person who may share my general interests but with whose opinions I personally disagree and who I find to be a poo-poo head". "Fangirl" is generally not derogatory. It tends to be used with a positive connotation. I'll be happy to be proved wrong in this claim. Anyone?