Bullet proof coffee (BPC) is a practice of adding some fat like butter and cream to your coffee. By doing this, you are basically providing energy to your body through fat and the caffeine activates your CNS. Does it help in fat loss? Depends. At the end of the day or in the long term, if you are consuming BPC and in a caloric deficit, you will lose weight. If not, you will not lose weight. As simple as that!
Looking at BPC exclusively for fat loss? Maybe not a good idea. It is the classic case of eating 3 slices of pizza followed by a cup of green tea. As green tea burns fat, apparently!