Universally, it is considered a bad idea to invite a vampire into your house. The thing with universal truths is that they are usually wrong, or at least highly inaccurate. There are worse things you can invite into your house, like Werewolves and Elves. Vampires will at least leave again.
Werewolves are essentially big, homicidal, kind of stupid dogs. If you invite one in it will not leave again, inviting it in is adopting it. You will forever be cleaning up dog hair and shredded clothing. It will not eat you though, because you let it stay, but cleaning up the “presents” they bring home is often unpleasant.
Elves do not leave, but they will make you leave. They are the worst kinds of roommate. They eat all your food, leave wet towels in the bathroom, have loud parties on weekdays and they smell surprisingly terrible for something that is very pleasant to look at. When they have had enough of your complaining about their terrible habits, they will exert their glamour on you to make you decide to leave.
Vampires on the other hand will just come in, suck some blood and then leave. They do not want to kill you, you are now a valuable source of sustenance. They will just visit on a regular basis for a little tipple. They don’t make a mess, they clean up after themselves and they do not stay past their welcome.
Now, I am sure there are some who would like to uninvite the vampire once they have accidentally invited one in, and this leads us to another apparent universal truth.
Garlic. You may have heard that garlic is an effective defence against Vampires, this is, however, inaccurate. Vampires could not care less about that wreath of garlic you have hung on every door, or the boughs of garlic across every window, or even the bulb of garlic in your pocket. None of these have any effect. However, if you eat a lot of garlic, like the kind of amount that makes you unpopular with work colleagues and family members. Eating lots of garlic changes the way your blood tastes, it makes it highly unpleasant to your fiendish friend. After a couple of garlic laced meals, they will cease to visit, preferring more pleasant appetite quenches.
While we are about untruths about our Vampire friends, let as consider the one about them not having a reflection in mirrors. This is a source of much amusement to Vampires. They do have reflections; how else would they be able to dress so incredibly well? But Vampires can move fast, blink of the eye fast. So, when you turn to the mirror they move, when you turn back, they move back. Vampires love a good prank, and humans are easily fooled.
Like how humans think Vampires can turn into a bat. This is clearly not logically possible, there is a mass differential that is impossible to overcome without large amounts of globules of remains and an inability to turn back into a Vampire. They could potentially turn into a cauldron of bats (yes, that is the collective noun!), but it is unpleasant to have your mind split into many pieces and putting it back together correctly is difficult and prone to mistakes.
Vampires can change form, but they go for much larger options, and their favourite is a testimony to their love of a good joke. They turn into large wolves. Which pisses off the Werewolves. A lot. This is the source of the conflict between Werewolves and Vampires. Werewolves, we have already established, are stupid and do not appreciate jokes. Vampires love jokes and annoying their furry friends is high on their list of pleasant activities. So if you happen to invite a Vampire in wolf form into your house you are lucky, it will leave after you feed it. You might need to supply it with some clothes though. Clothes do not make it through transformation, which should be kind of obvious, but apparently humans are kind of stupid too.
So, dear reader, I am guessing you are wondering if there are any benefits to inviting in a Vampire? Humans love a good exchange. To this I say, yes.
Number one, a regular hickey on the neck will make your friends think you are getting lucky.
Number two, Werewolves and Elves avoid Vampire friendly houses, so no risk of a homicidal pet or vile roommate.
And number three, which is probably what humans would consider the most beneficial, Vampires pay for their meals, and they pay well. They want you to let them return regularly. Keeping your Vampire happy is literally money in the bank. Think of Vampires as your occult sugar daddy. Yes, you will be a little tired and a little anaemic, but your bills will be paid.
So now that I have corrected some universal truths I need to go take my iron supplements and have a nap.