Question: what is the worst invention ever?

Andrew Scott answered on 25 Jun 2015:

Margerine: It tastes bad. It’s usually a hydrogenated vegetable oil. This hydrogenation makes it worse for you than other fats. Eating these fats can increase your risk of cardiovascular diseases (mainly heart attacks and strokes).

There are some pretty awful things invented for war: Sarin gas, napalm, hydrogen bombs.