Sure you can! Don't you know how to talk yourself up, mate? You just have to tell the story in a way that makes you sound humble. Here, rule number one,

[ Sirius holds up a single finger between them, looking at Harry very seriously. ]

Never make it sound like you're trying to impress anyone, even if you are. I don't go around saying that I was one of the youngest and top performing aurors in my division of all time, because that sounds like bragging. You wait until they ask, and you slip it in there. 'Oh, are you free tomorrow?' Oh, I can't tomorrow, I've got a silly thing for work, but I can do Friday. 'What do you do?' I'm an auror, it's a bit of an award ceremony, it's nothing special, bureaucratic nonsense, you know how it is.

[ After he's finished, though, he snorts a laugh, partially at himself and partially at Harry. ]

They don't really call you that though, do they? I understand that there's a flair for dramatics but bloody hell, how do you not hit people?