Dead pig is not afraid of hot water.

死豬不怕開水燙

[PinYin] Si3 Zhu1 Bu2 Pa4 Kai1 Shui3 Tang4

A dead mouse feels no cold. (Homologous English Idiom)

Immersing pork into hot water is an essential step before cooking it. If the pig is still alive, it may struggle and scream loudly. If it is dead, it is not able to sense the hot water.

You can use this slang to describe someone who appears to be unscrupulous, regardless of anything. It is a little rude though, since in Chinese culture pig usually refers to a negative meaning.

Example:
他的醜聞又多了一樁，但是本人一副死豬不怕開水燙的樣子。
There comes another scandal of him, but he himself seems not to mind at all.