Why was Victarion so freaked out by this?

Victarion doesn't seem like the type who gets put off by things easily, but while having a conversation with Euron he thinks of his brother's nakedness as "obscene and disturbing."

Euron turned to face him, his bruised blue lips curled in a half smile. "Perhaps we can fly. All of us. How will we ever know unless we leap from some tall tower?" The wind came gusting through the window and stirred his sable cloak. There was something obscene and disturbing about his nakedness. "No man ever truly knows what he can do unless he dares to leap."

This is really strong language - I searched the books and nothing aside from this is described as "obscene." What freaked Vic out so much? He's probably seen him naked loads of times already, right?