Dizemos que a pessoa "é uma santa" sarcasticamente exatamente com o sentido contrário. Em inglês:
holier-than-thou = behaving as if you are morally better than other people, in a way that annoys them, a person who is obnoxiously pious or self-righteous.
→Example: I’ll curse them however I want. Those trying to stop me from hurling abuse [at the Japanese], what are you thinking/who do you think you are? You sanctimonious hypocrites, being so holier-than-thou.