Ninja - Ninjas are zombies that manage to come up behind you, regardless of how much you check behind you, how closely you listen, and how many teammates you've got covering you. Somehow, despite checking that corner 10 seconds ago, there's a zombie popping out of there, completely silent, beating on your spine.
The Arcer or The Curveball - The standard zombie formula is this: Stand around unaware until startled, then charge the survivors in a relatively straight line. But occasionally you'll get a crafty one.
If 1 is the starting positions, and 2 is the standard zombie path, 3 is the Arcer. For little or no reason, sometimes zombies will swing around the side and try and flank you. When in small groups, this doesn't present much of a problem, but when you've got some coming straight at you, and a couple curveballing you from both sides, it turns bad fast.
The Theatric - I rarely actually use this name, but I definitely see them a lot: zombies that just won't fall down unless they add that flare of melodrama. Sure, you hit them square in the chest with the hunting rifle, and they're most certainly dead... but they want to wave their arms around and imitate a Shakespearean actor before the hit the ground. Tend to waste a lot of ammo on these.
Any (loving) nicknames you guys have come up with for regular zombies? Or just me..?