Other 'weapons' that I am allowed to take on board? My PC. Now mine is a small unit and weighs only 1kg but what about the big Dell and Compaq units that weight 3.5 kg? Swing that at someone's face/back of their head and they would probably notice!!
Also, a bunch of keys (door + car) very nasty. Many others have already mentioned that I can buy a 1 litre bottle of spirits on board, once again, if I swing that at someone's head they will realise it.