Straight: Vampires are rather kind and don't want to harm people.
Vampires are bubbly and affectionate and act like cheerful little girls.
If it weren't for the fact it's 3 AM and Alice had just told Bob such, you'd never guess that Alice was a vampire and you'd never know she's struggling with her hunger, because of how friendly she's being to him.
Vampires, like everyone, can choose to be good or evil.
Vampirism is a disease that affects otherwise normal people, and it has no logical reason to alter their personalities.
Because of all the negative stereotypes from horror movies and scary stories involving vampires, trying to be on good terms with ordinary humans can make vampire life easier.
Vampires have to get blood from one who is friendly to them, and don't need to feed very regularly, so being polite and friendly makes their desires more understandable but also allows them to feed from a willing volunteer.
They are only coping with they curse by attempting to rationalize it.
Parodied: A vampire tries to clean up his act, and ends up encountering a series of absurdly violent events, which leave him comically failing in his goal.
Zig Zagged: Nobody's quite sure if the vampire's really friendly, or if he's just waiting for the right time to strike.
Averted: Vampires aren't friendly creatures at all.
Enforced: It's a kids' show, so there can't be violence, but they want to include vampires anyway.
Lampshaded: "You're rather nice for a vampire."
Realizing how mean the rest of his kind are, a vampire decides to be friendly just to be different than the rest.
Vlad does not particularly feel like chasing down screaming victims, and he really doesn't want to have a stake shoved through him, so he opts for an honest night's work and getting blood from willing donors. It's hard sometimes, but at least he can still look at himself in the mirror... at least metaphorically, if not literally.
Defied: Asked to try being nice for once, a vampire laughs at the idea, refuses, and goes back to killing people.
Discussed: "Why're you so kind? Aren't vampires supposed to be mean?" "Well, I guess I'm just different."