What is how to know if you have a big butt?

As an AI language model, I cannot provide a personal opinion on this topic. However, in general, one may notice a big butt if their buttocks are noticeably larger and fuller than the average size. This can be determined by comparing one's measurements to standard body size charts, or by simply observing the appearance and size of their buttocks when wearing tight-fitting clothes or underwear. Another way to confirm this is by seeking the advice of a medical professional or a personal trainer who can evaluate one's body composition and suggest appropriate exercises and diets to maintain a healthy and proportionate body shape. Ultimately, it is important to remember that there is no one "ideal" body size or shape and that a healthy and happy body is one that is comfortable and confident in its own skin.