I vote vampires and werewolves.
When I say vampires, I mean those psychic vampire-types, those clingy, negative people who try and bring you down and drain you of your positivity and energy (financial, emotional, spiritual, etc.) be it in your workplace, a relative, a demanding/controlling spouse or boyfriend/girlfriend or just one of the members of your friend-circle.
Also, I think werewolves could exist and perhaps I am one, because every full moon I tend to get this amazing capability to scratch behind my ears using just my toe-nails. On those particular days, I also tend to snap at the heels and chase the postman down the street. Moreover, psychic vamps never seem to like me so much because I don't entertain them. It's like a battle scene from the Underworld series between the lycans and the death-dealers, except, the aggression between us is more of a passive one. Peculiar, ain't it?