For context, G-man is proclaiming his brother as the Emperor of Imperium Secundus (the worlds that got cut off from the rest of the Imperium by a huge Warp storm). Sanguinius isn't exactly thrilled about it, but knows he's the best choice for the job as they have no idea how to get out and if Terra even still stands.
Oh I'm aware of the context. It's just a very silly picture.
Also it is amusing that he's doing the same damn thing again almost immediately after being revived.