The phrase "be big about" usually means to show maturity or generosity by being forgiving, understanding, and magnanimous. Therefore, antonyms for this phrase would be to be petty, vindictive or resentful. A person who is small-minded, narrow-minded or selfish might have difficulty being big about something. Antonyms for "be big about" could also include words like stingy, uncharitable, or unforgiving. These words describe someone who is incapable of magnanimity, unable to let go of a grudge, and unwilling to show mercy. Thus, if someone is asked to be big about something, they are being asked to show grace, resilience, and kindness, rather than pettiness, malice, or spite.