Question

what the name of a character trait for someone that is "Hard" on the out side but "Nice" or "Soft on the inside?

Answer 1

You could say that they are a sheep in wolf's clothing.

Answer 2

There's not really a word for it, just phrases. You could say that person is stubborn or abrasive, and you can also describe them in a nicer way just pointing out who they are on the inside.