One of our most controversial posts ever was "Torture vs. Dust Specks".  Though I can't seem to find the reference, one of the more interesting uses of this dilemma was by a professor whose student said "I'm a utilitarian consequentialist", and the professor said "No you're not" and told them about SPECKS vs. TORTURE, and then the student - to the professor's surprise - chose TORTURE.  (Yay student!)

In the spirit of always making these things worse, let me offer a dilemma that might have been more likely to unconvince the student - at least, as a consequentialist, I find the inevitable conclusion much harder to swallow.