For the less culturally enriched, it is referring to the practice of the Brit milah. It is the Jewish tradition of swallowing the blood directly from the wound of a circumcised infant - complete with transmission of infectious diseases.
Yum!
Jew: Nice Dracula costume, man!
Dracula: Thanks! Who are you supposed to be?
Jew: Oh, I'm also a vampire
Dracula: Er, what?
Jew: I just don't bite 'em on the neck.