Luke was grateful for the blush to go ignored, if only because he was pretty sure he was supposed to have more composure than all that. He didn't always, he wasn't emotionless or anything, he just ... tried to uphold a look that people expected of him, was all.
Still. He smiled and it was a little lopsided and all good natured. "Maybe not sir? Rey calls me Master Luke. I think that'll do fine. Let's meet sometime next week." In the mean time, Finn could have all the sugar he wanted and maybe go hug his friends until they were blue in the face. Luke had to revise some lesson plans.