What defines "Looking an Enderman in the eye"?

In Minecraft, when you look an Enderman "in the eye", it will aggro the mob. But what determines "Looking him in the eye"?

• Where does the cursor have to be?
• How far away can you be?
• Can I "look through" blocks like glass/water/leaves?

Solution 1:

Anywhere from the knees and above will aggro the Enderman. They will aggro from as far as 64 blocks away. Except for water and lava, looking through any type of block will prevent the aggro, as well as wearing a pumpkin on your head. If you're trying to aggro an enderman, the easiest way is to look at the torso, as it's the widest area; also, you likely won't be looking too high, as is more possible when aiming for the head.

Looking at an enderman's feet will not aggro him. The best attack method, then, is to get close to them (or aggro them so they teleport to you) and then look at their feet and attack with melee. Standing under a two or 2.5 block high shelter will keep them from hitting you, since they are 3 blocks tall. They will not teleport away, and can be treated like a zombie at that point, continuously attacking as they advance until they die.

They cannot be hit by a ranged attack, including damage or poison potions, even if the cursor is not hitting the enderman when the shot is fired/potion is thrown. They always teleport away before taking damage.