Just about as difficult as humor.
Given that we don't have AI, you can statiscally analyze all you want, a CPU is not going to "understand" what is being said.
I agree that grammar correctors have come a long way and that's a good thing, but the computer is not understanding anything, it is just reacting to a set of rules.
Humor ? That is as far away from CPU comprehension as FTL travel is for us meatbags.
Because nobody can accurately calculate humor.