Bucky thinks that Steve is attractive naked. Hell, he's had a bunch of wet dreams about that naked body and jerked himself off more than once growing up to the idea of being naked with that naked body. Not that he can ever tell Steve this, because then he'd have to hurl himself off a cliff for revealing embarrassing secrets to his best friend.

Penny pushes her nose against Steve's leg and gives a loud huff in warning that if Steve keeps pushing at her human and touching him when he hasn't given the okay, then she's going to have to take more drastic action.

"--Steve, I look like a horror show if we're talking about naked now. So shut the hell up, or I'll show you what people looking disgusted by a body look like."

Terrified as he is to show his body to doctors, he will strip naked right alongside Steve and show his scars off to everyone just to make a point to his best friend. It's the way he's always been, something about Steve effortlessly makes him able to push his boundaries.