How would one say: "You should be ashamed of yourself." in Mandarin and Cantonese?
Mandarin:

你应该为自己感到羞耻 we still say it in general and it is much mild comparing to 你真不要脸

Cantonese:

In Cantonese we would say 你应该感到羞耻 but it is more formal, in slang/daily i usually say 我系你我會搵窿捐

Reference: I am a native speaker for both