Sirius grinned and nodded, letting the joking tone last though he wasn't blind enough to miss the truth in that statement. "Just don't make a habit of that, or I'll have to remind you that you're not that person." He said it with a bit more enthusiasm and teasing than he might normally, but didn't feel the need to make this into a moment - especially with Lily there with them.
"We were put in Gryffindor for a reason, I don't think Prongs or I can be blamed for living up to the expectations put upon our shoulders at such a young age." He even managed to get through all of that with a straight face, though he couldn't help grinning when he'd finished.
Sirius rolled his eyes. "Yes and that's why we made sure that you had it perfected, though I never did understand why she didn't believe me. I have an innocent face, more innocent than some people at the very least."