A man riding the bus, must stand because there are no seats. On the bus he meets a man with one arm, who pulls a gun and kills him.
It's because losing an arm makes you mean and dangerous.
Of course of you lose BOTH of them, you are then completely 'armless...... <img src="/ubbthreads/images/graemlins/stupid.gif" alt="" />
(Sorry, that dreadful joke may not work for non English speakers... <img src="/ubbthreads/images/graemlins/think.gif" alt="" /> )
BTW, Bean's version is excellent - and IMO better than a 'real' answer that I read somewhere else. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" /> Maybe there are several versions of this one, as the answer I saw was quite ridiculous.