What is according to you the worst invention of Mankind and why ?

I feel "Mirror" as the worst invention, for that is when Humans started becoming selfish by looking more at themselves, as against nature's intention of an eye through which we can look at the other, and not as much at ourselves.

Sure all would agree, that without mirrors, it is definitely impossible to have a look at our back, or our face. So can we say Nature wanted us to take care of others more than ourselves.. and be taken care by others. ?