"Vampires Go to a Bar" joke

It's Halloween and everyone's out trick-or-treating. A bartender is working the late-night shift at the bar. He looks outside and sees everyone in crazy costumes. He sighs and picks up a glass and starts cleaning it.
At around midnight, a guy in a vampire costume walks in and sits at the bar. He says to the bartender "Hi. I'm a vampire and I'd like a cup of human blood please."
The bartender looks at him skeptically. "No you're not. You're just wearing a costume."
"No, no, really," he insists. "I'm a vampire and I'd like a cup of human blood please."
"Alright," the bartender says. He goes in the back and comes out with a cup of blood. He gives it to the vampire who drinks it right away.
"Thanks," he says, and leaves.
An hour later another vampire comes in and sits at the bar. He says "Hi, I'm a vampire and I'd like a cup of human blood please."
"Okay," the bartender says and goes in the back again. He comes out with another cup of blood. He gives it to the vampire who drinks it and leaves with a 'thanks'.
An hour later a third vampire comes in and sits at the bar. "Hi," he says to to the bartender. "I'm a vam..."
"I know, I know," the bartender interrupts. "You're a vampire and you want a cup of blood right?"
"Um, no," the vampire answers. "I AM a vampire, but I'd just like a glass of hot water please."
"Sure" the bartender says. He pours him a glass of hot water. As he gives it to the vampire he says "You know, there were two vampires that came in before you that wanted blood. How come you're just asking for water?"
Without answering the vampire reaches into his pocket and pulls out a used band-aid.
"Tea time."