That person, place or thing that destroys you. The thing that brings you to your knees. (and not for that reason).
This is the experience or thing that always ruins you (at least temporarily) until Lois or Jimmy comes by to help.
This is the thing that you dread, yet expect, and the makes me cry everytime experience. We often like seeing this in other people, because it makes them look human. But we often keep this from others, especially if you are male, since it makes you look weak. The great irony here is:
we are machines without this and helpless with it. You choose.
see also, song: pocket full of kryptonite
see also, sequel: My own personal Kryptonite