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.
arbitrary - Based on random choice or personal whim, rather than any reason or system

She felt that when the judges chose her competitor as winner of the debate, that the decision was totally arbitrary, and didn't recognize how well she had really done.