A Butt-Monkey is someone who worships another person.
They laugh at all their jokes whether they're funny or not,
they think they're great even when they're not and generally strive to
spend as much time with that person as they can.
The person the Butt-Monkeys follow is called a Butt-Monkey King or Queen.
http://www.urbandictionary.com/define.php?term=butt+monkey