"Dost a turn" is an idiom that means to perform a favor or do something helpful for someone. Antonyms for this phrase could include "ignore," "neglect," or "decline." If someone chooses to ignore or neglect another person's needs, or declines to do them a favor, they are essentially doing the opposite of "dost a turn." Other antonyms could include "harm," "wrong," or "betray." Those who harm, wrong, or betray others are acting in a manner that is opposite to the helpful and cooperative spirit that "dost a turn" implies.