He took the offered seat with the usual Black grace, like he was taking a seat at a state dinner, rather then in Remus' flat. He relaxed his posture a moment later though, and slid a glance towards Remus. "Thanks. I don't think I realized how hungry I was."
Shy and polite were not things Regulus could have afforded to show when he was in school. They weren't traits that would help him in any way, and would have, in fact, left him vulnerable.
He didn't have anything left to prove any more, and it made quite a bit of difference. Remus was either going to trust him- or not. Just as Sirius was either going to forigve him- or not. Harry was going to listen to him- or not. Regulus was done, for the most part, trying to make the world around him fit itself into a neat little box.
Well, mostly. That didn't stop him from trying to keep his own life in strict order. As evidenced by the neat, almost compulsive way he laid out his sandwich on a paper napkin, edged lined up perfectly, and chips carefully portioned out. The Coke he took with definite eagerness. Caffeine and potions work wasn't the best combination, but it was one Regulus indulged in regularly.