Vlah is a term that is mostly related to vampires or vampirism. It can also mean something mildly gross or disgusting happening to a person (kind of like blech).

IRC Usually intended as a mildly sarcastic indication that the person who is saying it has just heard something ridiculously goth. Originally: The goofy sound that Bela Lugosi made as the bloodthirsty Count in Dracula: ("Vlah! I vant to suck your blood!").