Hiddleston's impression of Jeremy Irons..

.. in the tavern scene was fantastic! 

I've never seen a Hal actually do such a skillful impression of the actor playing his father in this scene. I did a youtube search of "Hiddleston impression" and apparently it's a thing of his, doing impressions of people, and he's quite good at it.

The second time I watched this, I also noted a funny little reference between the tavern scene and the one where Hal goes to see his father after being summoned. Hal, playing his father, makes a motion with his hand, asking Falstaff, playing Hal, to come closer. And then in the next scene you have the real Henry IV, i.e. Irons, doing the exact same motion, asking Hal to approach. At this, Hal sort of smiles to himself, as if remembering the charade of the night before. Great little detail.