Answer: B. Treacherous fiends
Explanation: None of the other options can be understood as insulting anyone. Treacherous is a strong adjective with negative connotations to describe someone who has betrayed or is willing to betray others (a much stronger choice of words than, for example, disloyal), and fiend means demon, i.e., a person so vile that one must suspect whether he or she is really human.
