披着狼皮也是只羊
[pī zhe láng pí yĕ shì zhĭ yáng]
Under a wolf's skin, I'm still just a sheep. By taking on a tough or fierce exterior (like a wolf), he/she remains gentle and weak at heart (as a sheep). In other words, this person appears tough but is actually soft inside and not as intimidating as they may look on the outside.