"I never doubted that someone would know himself. I stated that I like myself. Very different. Do you not know yourself or do you not like yourself?" he asked, knowing that this was something he would have never asked a Slytherin, because no Slytherin would have answered, but Gryffindors could be a lot more entertaining with their need to share.
Regulus raised an eyebrow. "A Gryffindor who's not a bright and shiny optimist. You must be a rarity." He was also a puzzle, because Regulus couldn't understand how these types of answers matched with Sirius' carefree attitude. "Should I ask what makes you so different or just accept that you might - only might - be tolerable after all? A trait I don't usually associate with Gryffindors in general, and Sirius' friends in particular."
He smiled at the answer. "Now, that's just another bonus, and of course, clear it with him. I'm sure he'll enjoy the suggestion." Regulus nodded. "Of course, they couldn't possibly learn what I know anyway. It takes years. However if it makes you feels more comfortable, we can always demonstrate first. You are the professor; you should be able to defend yourself, and it makes it for a much more interesting lessons when you see two duellists who don't have to hold back because of international rules or pesky things like school regulations. Want to play with me, Lupin?"