Endermen already attack the player if the the player looks at them, but what if the attacked anything that looked at them? It would be interesting to watch an enderman attacking a curios pig, or perhaps in a stand-off with a suspicious creeper. This would also add a bit of mystery to the game. What could be so important that the endermen can't let anything see it?
Don't like, if they fought with creepers it would be entirely possible for you to mine in your fully lit and safe tunnel and still find that your world is a crater. Fighting with a pig would also make it more noticeable and since passive mobs will be consistent it would suck.
Checking already gives you 25% addiction.
"a mysterious set of lights have been seen to the north/east/south/west!"
and then they would come...
GODDAMN IT
STUPID GENDERFLIP VIRUS