Reese's peanut butter cups are great. They're my favorite candy. But, saying that they are the greatest invention in the history of mankind is absurd. Just off the top of my head, here are some more important inventions: soap, the wheel, air conditioning, refrigeration, airplanes, antibiotics, writing, and on and on and on.
Reese's is definitely not the greatest invention from mankind. I like the candy as much as anyone else, but there have been cures to diseases invented. Cars, telephones, airplanes, and computers have all been invented. A candy that tastes good does not compare to saving millions of lives because of a scientist or doctor's invention.