What do they call human who like vampires to feed off them?

They call them donors.

I find 'donor' to be a rather antiseptic term, void of any interesting connotations. I much prefer the Victorian term 'thrall' derived from the Scandinavian for slave.

They can be called donors or black swans. some call them feeders.

Sometimes the humans are also referred to as "pets", "sheep", or "cattle." It probably would depend on the vampire. Some vampires would use more derogatory names than others.