Luke doesn't watch him. Because he's making a point. Just like how he just crosses his arms even more and scowls even harder when he feels the weight of the other man's stare.

Not today Satan! This might just be a small, insignificant battle in a much longer war, but Luke has every intention of winning here. He'll worry about the later, later. Right now he's making a point.

And that point is, he's totally not listening to you. Or afraid of you. He absolutely is And you can't tell him what to do!