I don't see why bronies can't take a joke, and haters take this phrase seriously. I mean, Gabe Newell likes the show and he put this line in as a joke. This is almost the same as the haters whining about the unicorn hoodie. I heard it was more inspired by Robot Unicorn Attack.
So true, Heavy. Also, you are the only one who can made a fairy princess outfit look manly. And thanks to that line, an awesome GMod animator was able to make his GMod freak say, "Friendship is Magic is NAHT DAT GOOD! Bite me, bronies!" So that line is good for something, at least, even if it is a reference to a shitty little kid's cartoon about colorful ponies.