This is an alcoholic drink made by mixing a shot of raspberry schnapps with a glass of sparkling wine. Mostly, teenage girls who want to get drunk but don't like the taste of alcohol seem to enjoy this beverage. It's sort of a home-made cooler.
I had never heard of it when I was young, but I bet teenage girls have been making them for years, and only started calling them Vampire Slayers after the tv show Buffy the Vampire Slayer became successful. The name could last longer than the show. We still call the children's drink a Shirley Temple or a Roy Rogers, even though kids today don't know who those people are.