So I was playing a volibear with Zilean and I had the passive-Armored Bear Hater icon with the text: "In my day, we would never have allowed an armored bear into the League of Legends." Why does Zilean hate Volibear?

One moment. The person who Zilean is based off of Zileas, thought the idea of a bear champion bring brought to the League was stupid. The office was jokingly divided into two sides, Volibar's side who wanted an armored bear, vs Zileas who didn't. As you know, Volibear WAS released so as a joke, they both have hidden passives where they are against each other in game. (Does not work if they are allies). Zilean gets "Armored Bear Hater" which is a picture of Volibear's passive crossed out while Volibear gets the Chrono Keeper Hater which is Zilean's passive crossed out. If Zilean kills Volibear, he gets +10 gold. If Volibear kills Zilean he gets +11 gold and says one of two quotes: "Your time has run out, Chronokeeper" or "I got a special claw for you, Zilean."

http://www.youtube.com/watch?v=_0bGp6BwWaw

Here is a video, I hope that clears everything up.

Hey I was playing with you when, we mentioned that lol

Its also a tribute to the move "Golden Compass". Zilean's clock looks like a compass and Volidear is obviously Iorek Byrnison Pic