Aggressive enderman tag with /summon?

How to spawn a aggressive enderman?

I am making a slenderman map and want to use /summon to spawn slenderman (enderman with a texture pack). I don't know the data tag.

There's no NBT tag for this.

From this thread on the Minecraft Forum:

Endermen do not have any extra NBT tags for doing something like this. Endermen attack based on player input; even if we could manipulate whether they were angry or not, there wouldn't be a way to target an unknown player.

A possible workaround would be to force the player to briefly look the enderman in the eye by spawning him directly in front of the player.

The wiki has a list of all NBT tags per entity.