Lol. Well, no, personally I don't believe in vampires. Although I do have two pointy teeth that reminds most people of vampires, I do not feel the need for blood, nor have I died in this life yet. Or so I hope

I think there are some people who want to be different so bad that they start to drink blood, and after a while of doing so, it becomes something like an addiction, comparable to a drug addiction. A human being doesn't need drugs to survive, but when frequently used, the body gets used to it and will find a sudden stop strange, and will react to this. Same goes for blood addicts.
Plus, if you drink too much blood, you can die. And since people are led to believe that vampires need blood every 12 to 24 hours, it is impossible for a live human being to imitate this, for it'll become their deaths.