Adjective
reprehensible - Describing behavior, actions, or conduct that is morally wrong and worthy of disapproval or condemnation.
Though he told people not to repeat it, it was reprehensible for him to spread rumors about his colleague, knowing it would damage her reputation.
unforgiving - Not making an allowance for error or weakness in others; not willing to forgive others for things they might have done wrong.
Because they knew that Alaska in the winter is an unforgiving environment, they had to plan their expedition very carefully.