I tend to divide them into three categories: Actual haters, people poking fun, and trolls.
If it's an actual hater, I try to logically explain that I realize why they don't like the show (ie: every site they go on now is full of ponies), and leave them with their opinion. If it's just people poking fun I tell them to try watching it for a change. And if it's a troll, I'm just really condescending and smug towards them.