What happens when immovable object meets irresistible force?..?

In the USA they call it an election.

There are no immovable objects or irresistible forces. 

I think that probably those things exist only in the imagination. Incidentally, cedrick needs a refresher course in quantum mechanics, so he could get rid of the "atoms are mostly empty space."

Hurricane Katrina.

I think I remember back in highschool that we were taught that atoms are 99% empty space, so if there were to be a scenario where there is an irresistible force vs immovable object, the atoms would basically just pass by each other

We have this with photons and atoms.  The irresistible photon continues unaltered.  The immovable atom stays still.  The one passes through the other without interaction.

Something's got to give

I think you misstated that BUT E=MC^2 or in it's earliest form F= MS^2...

N.Shadows

By definition you can't have both.

Nothing. They cancel each other out.