>>1I tried to think of one, but the only thing I can think is similar.
USA releases one of its chimera viruses it's been sitting on since the cold war. Innoculates only its own desirable first, wipes out the rest of the worlds population.
...except that Russia and China both have them as well, and would do the same if they suspected that shit was going down, so still, no pass go.
Ten thousand vectors all leading to certain doom.
With any luck, I'll live long enough to see them pile up and work their magic firsthand. Couldn't happen to a more appropriate country.