What is the worst invention?

I think that the worst invention would have to be those jelly sandals. I remember when they were popular when I was younger and I know I begged my mother for a pair. I've noticed that the infamous jellies made a comeback a little while ago and I got a flash back of the discomfort I had endured as a child wearing those jelly sandals. The sandals are completely rubber and rub the backs of your ankles till you have blisters. These have got to be the most uncomfortable shoe ever created and that is why I think that jellies are one of the worst invention, and one of the worst fashion trends.