The phrase "be up about" means to feel cheerful, optimistic or positive about something. The antonyms for this phrase are "be down about", "be negative about" or "be pessimistic about". When we are "down about" something, we feel sad, low or disheartened. Similarly, when we are "negative about" something, we tend to focus on the negatives and have a gloomy perspective. Being "pessimistic about" something means that we anticipate the worst possible outcome and lack hope for a better future. Therefore, it's important to stay "up about" things as much as possible and try to maintain an optimistic outlook on life.