The fact that Agamemnon kills a deer in Artemis' sacred grove and brags about is even stupider than it sounds. See, the deer is a sacred animal of Artemis and is symbolic of the goddess herself.
She loved them so much, she was even said to have a chariot pulled by deer with golden antlers. So, when Agamemnon slays one of her favorite animals in one of her favorite places, it's a major slap in her face.
In some versions of the myth, a deer comes into play later on when Artemis switches Iphigenia out for one of them right before she's about to get sacrificed. We wonder why the goddess would provide a deer as a sacrifice to make up for the fact that another of her deer was slaughtered. Is it just us, or do the deer really get the bum end of the deal in this myth?