How about if my wish is that my best friend never dies how would that work, because that would benefit me. I couldn't possibly imagine a situation that would require me to kill my best friend. Well not that I couldn't imagine the situation in fact I can think of a few but since he specifically said the only person who can benefit from the wish would be myself it excludes those situations.

Other than that I would gladly sacrifice myself for my best friend , that is if I had one.