Perusing YouTube for "real vampire" comes up with close to a dozen different variations. The three major "species" seem to be "sangs", i.e., sanguinary vampires that drink blood, psychic vampires that drink life force, and lifestylers who like a look that is somewhere beyond gothic. All three groups sometimes have fangs and sometimes do not.
In psychology and criminology, "vampire" is a term informally used to refer to psychopaths or narcissists in various contexts. On one end of the spectrum, it concerns the habit of such people to leave long-term friends and family emotionally drained, due to years of subtle- or not so subtle- psychological or physical abuse, and to their needs for attention, adoration, fear, or control. At the other, it sometimes refers to serial killers.
Cutaneous porphyria is a genetic disorder that causes photosensitivity, blisters, and necrosis of the skin. Some science writers have casually presented it as the cause of werewolves and vampires, while its real world sufferers received misplaced criticism and stigma.
Renfield Syndrome is a mental illness whereby the patient believes they are a vampire, or that they are becoming one. They usually suffer from schizophrenia and it tends to be a symptom, meaning that proper treatment can put the delusion under control.
Named after a character suffering from a similar condition from the novel Dracula.
Hematophagy is the practice of some animals that feed on blood for their diets.
The scientific name for the blood-thinner in their saliva is called "draculin."
Several kinds of internal parasite.
Butterflies may do this.
Spiders could considered as vampires too, since they're unable to ingest anything but liquid food. Depending of the species, they can suck dry their victims after pumping in the holes perforated to inject them venom gastric fluids, leaving behind their more or less intact husk, or can grind them to pulp with their chelicerae while injecting digestive fluids and absorbing the liquefied tissues too.
UK Member of Parliament Peter Mandelson is often nicknamed "The Vampire" for his rather unnatural air and manner.
Some stars are kind of vampires, growing at the expenses of their companions. For instance, the famous Algol in Perseus,note curiously, the name Algol means "the ghoul" in Arabic where what was once the less massive star is now the more massive of the pair, having captured matter from its companion once it started to evolve to become a red giant. Taken to an extreme with pulsars (neutron stars) such as XTE J1751-305, which has stripped down its companion - a former star - leaving it with a mass comparable to that of a planet, or the case of EF Eridani, where a white dwarf star sucked matter off a companion star, leaving it as a stellar remnant that is difficult to classify. Sucking too much, however, can be very hazardous for the health of a white dwarf.
And let's not forget Black holes, the ultimate suckers of the Universe. At least if you get close enough to them.