Why is Sidney Crosby hated by fans of other teams?

Sidney Crosby is the captain of the Pittsburgh Penguins and whenever the Pens come to other teams stadiums, he is hated. Why is that? EXACTLY what does he do at every game, before every game, & after every game, on & off the ice that causes him to be booed at a lot by those who hate him? For the record, I am not a Pens fan, I'm an Anaheim Ducks fan.