A lot, unfortunately.

I dated this girl who suddenly became obsessed with vampires a few months into our relationship, and began to identify as one. At first, I didn't really care because I have grown up with self-identified "vampires" since elementary school, and they grow out of it eventually. I also knew about vampire lifestylers, and the fact that they have pretty strict rules about consent and how to do this shit as safely as blood drinking can possibly be. (Which is still not very safe, but whatever.)

She was not a vampire lifestyler. She was okay with cutting herself in front of people who selfharm, pressuring other people to let her drink their blood when they were not comfortable with it after I personally declined, and would not disinfect any tools she used. She also drank her blood and then kissed me afterwards, and would not quit kissing me when I was trying to get her off of me. She had also displayed stalker-like behavior to someone close to me for 6 or 7 months straight because they "smelled nice" and she wanted to taste their blood. Later, she started admitting she was craving human flesh too, and would say creepy things about wanting to rip people's throats out.

She wanted to try blood play with me. While I didn't want her to cut me, I gave in and cut her. I was not aware that I had a fear of blood, and I think her behavior gave me that fear. While I never cut her deep, the small bit of blood disgusted me more than larger quantities of blood I had seen or came in contact with in other points of my life.

I do not think she is a vampire (obviously), though I definitely believe that she may be a sexual predator, and a regular predator too, I guess. While I trust that real vampire lifestylers are not like her at all, I would rather limit the amount of times I come in contact with blood to first aid and first aid only.