Its a way of saying "it'll kill me."
ie: they are trying to 'do me in.' -they are trying to kill me.
ie: These cigarettes will 'do me in.' -these cigarettes are gonna kill me.
A purpose needn't have a meaning as it is a way of obtaining an object. It would be the object that would have or have not a meaning.purpose don't have any meaning as it itself is a meaninganswered...