Anybody working near or around a zoo knows that the giraffe is the most dangerous animal to work around and is responsible for a significant number of caretaker deaths and injuries. The giraffe covers ground so quick by the time one realizes that one is being attacked, its over. The only time I ever worked on a giraffe was after it had been darted.
I have seen clips of them fighting with one another by banging their necks. The torque that they create is amazing. If they connect with a human I would expect that you might get whapped about 40 feet or so.