وقتی به کسی میگن مار خوش خط و خال به انگلیسی چی میشه ؟

snake in the grass

someone who pretends to be your friend while secretly doing things to harm you.

examples: It's upsetting to learn that someone you once viewed as a good colleague is in fact a snake in the grass.

How could I ever have trusted that snake in the grass?

John is such a snake in the grass.