"I try." Mack's doing that thing where he's not actually smiling, but if you're observant, you can almost tell that he might like to be. It's possible that it could easily be missed, of course.
"I worked my way up through the marine corps," he says, adjusting his stance to something more along the lines of 'at attention'. "'m used to command -- I can grunt with the best of 'em, though."