I think it would be kind of funny if Kallus in his Imperial days was very aware that he's attractive. Then he joins the Rebellion and learns about the notion of being ✨humble✨ in addition to having his looks be way less relevant. The Rebellion doesn't have a dresscode and are nowhere near invasive enough to care about his facial hair or hairstyle. Overall, he doesn't have to apply as much effort to his looks and as such he sorta just... doesn't think about it as much. Until one day he's looking in the mirror and it hits him how different he looks. Way less put together - in the Empire they'd definitely refer to it as letting himself go. He still feels the same. Still feels attractive. But even so, there is this nagging feeling at the back of his mind telling him that he isn't. Not to others anyway. And it's not like it bothers him. Not really. It's just different. But it's not like it matters and he has got work to do. So he goes about his work knowing that he's no longer considered attractive. Except Kallus' idea of what's considered attractive has been heavily skewed by the Empire's standards. So while he's assuming he downgraded his looks to a solid Mid, every Rebel is having a moment of "wait, is Kallus not kinda very hot??"