[rspeer]

Perhaps not the hardest, but one where there's tons of room for improvement: the Story Cloze Test [1] is a test involving very simple, five-sentence stories, where you pick the ending that makes sense out of two endings.

A literate human scores 100% on this test. No computer system so far scores better than 60%. (And remember that random guessing gets 50%.)

[1] http://cs.rochester.edu/nlp/rocstories/

[johnlbevan2]

Interesting study; whilst it's possible to guess which ending is expected as correct, the alternate could be easily argued. For example, in the case of Jim's getting a new credit card, I recall during my uni days many students took that exact approach to debt...