This generally happens when you have a person, claiming to be a stoner, that is too scared to smoke marijuana while there parents are still awake. This usually happens because the individual thinks it is cool to be a pot smoker but they are scared of their parents finding out, so they only come out to smoke at night, much like a vampire would, this resulting in a "Vampire Smoker".
Jedidiah says "Hey Jepeto, its 420, lez get blazed foo"
Jepeto replies " I can't yet man, I am scared my parents will notice when I get home. But we can once they go to sleep, is that straight meng? You know I'm a true stoner."
Jedidiah exclaims " Hell nah, you a god damn Vampire Smoker like everyone else, I am going to find a true folk to puff down like charlie brown right now. I'm out."