Could be an incel's revenge.

If you could release a virus that would kill every single man on Earth, except for yourself because you would have the antidote, would you do it? You will be the only man left, with all the females. You would be able to have your pick of any beautiful woman you want, as well as having dealt vengeance on the men who took them from you. Imagine how satisfying that would be.

-eliot rodgers.