A lot of bad boys are like that, at least the ones on TV.
They're really nice inside, but don't know how to express it or how to deal with kindness directed at them. So they act all tough and macho all the time and can often look like jerks.
But inside they're soft and vulnerable and so sweet.
Mysterious princes are like that too, in a way, but it comes out different. Although there are some mysterious princes who consciously put up a vail of mystery to hide their activities. These are dangerous and mysterious and super cool (even if they do usually turn out to be bad guys

).
I think Yuki and Kyo would become violently ill if anyone tried to point out how alike they are. Then Kyo would try to kill Yuki, and Yuki would beat him up again.
