Hypothetically, what's the highest AC someone could possibly get? The point where it's imposable to go any higher. The point where, even though you're a complete abomination that's overspecialized like a guy trying to play a cleric like he was in WOW, you can just stand there, untouchable by anything except a natural 20.
Would it be a dwarf fighter battling a giant? A halfling monk with the dexterity of a god?
Or a rogue that's good enough to never get anything ****ed off at him?