Shooting an arrow up the nasal passage. Not a lot of Buffalo looking at you with their nose up during a charge. So, ......
1. Yes a proper arrow (etc) can penetrate the skull of a Cape Buffalo.
Cape buffalo (African buffalo) possess an incredibly thick, heavy skull, particularly in mature males. The frontal bone (where the horns meet) can measure from 2 to 4 cm (0.8 to 1.6 inches) thick. Including the fused, heavy layer of horn known as the "boss," total skull thickness at the crown frequently exceeds 7 to 8 cm (2.7 to 3.1 inches)
2. Hitting a moving grapefruit with an arrow is another thing.
3. If you are about to be stomped and your at full draw you might as well go down swinging.
In your next life. Practice being much quieter and more sneaking and just shoot them properly with your bow and avoid the extra effort.