Beaten so fiercely that most of his tail feathers fell out, the bird was euthanized, said Richard Gentles, a spokesman for the city's Center for Animal Care and Control.
"It's just unbelievable that someone would do something to a poor, defenseless animal and do it in such a cruel fashion," he said.
The peacock, a male several years old, wandered into a Burger King parking lot in the New York borough of Staten Island and perched on a car hood Thursday morning. Charmed employees were feeding him bread when the man appeared.
He seized the iridescent bird by the neck, hurled it to the ground and started kicking and stomping the creature, said worker Felicia Finnegan, 19.
"He was going crazy," she said.
Asked what he was doing, she said, the attacker explained, "'I'm killing a vampire!'"
Employees called police, but the man ran when he saw them. Authorities were looking for the attacker, described as in his teens or early 20s.
It was not clear how the bird made his way to the Burger King, but a Staten Island resident who raises peacocks said he had given some to a person who lives near the restaurant.