There's a good definition of cult films here. It begins: Cult Films have limited but very special appeal. Cult films are usually strange, quirky, offbeat, eccentric, oddball, or surreal, with outrageous, weird, unique and cartoony characters or plots, and garish sets. They are often considered controversial because they step outside standard narrative and technical conventions. Most cult films cut across many film genres (science fiction, horror, melodrama, etc.), although they can be very stylized, and they are often flawed or unusual in some striking way. They mention that Fantasia was considered a "cult" film for a while.

I'd agree with LH that much of the appeal of cult films comes from perceiving oneself to be part of an enlightend "cool" community, but I also think many fans simply have a real appreciation for their particular favorites.

As for blood, I'm sure I've seen people swimming in pools of blood in some film or other; more blood, but not as bright red as the elevator scene in The Shining. The grossest thing I recall seeing was open heart surgury on regular evening TV. Shudder. I lasted about thirty seconds before changing the channel, I never lingered again.