An adjective typically used to describe Vampires, Werewolves, Zombies, girls who bite you, and any vicious animal. It derives from the two words "dangerous" and "fang."
"Damn, that Jessica is Fangerous! She keeps biting random boys!"
"Oh woooww, That Bill Compton is so fangerous, I love how he looks when his fangs are out."
Oh geez! It's a snake! Be careful man! Those things are fangerous!"
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi