When you have any two things that are supposed to join together as one to perform a certain function and they don't fit together the correct way they are whompy-jawed.
If you are using a pair of scissors and they don't cut correctly and the blades shift and won't meet like they are supposed to then they are whompy-jawed.
This is either the Ohio or the New Jersey version of whopperjawed. I had only ever heard it my way until I started looking it up to find the derivation. I mention Ohio because that's where I am from, but my mother who taught it to me is from New Jersey, with relatives from various east coast places.