Robert Metcalfe is an electrical engineer from the United States. He's had a very accomplished career: He founded tech giant 3Com and coinvented Ethernet… you know, the thing that runs your hard-wired Internet.
However, he's made some incorrect predictions along the way. In 1995, he famously predicted that the Internet would suffer a catastrophic collapse the following year. He promised to eat his words if it did not. Of course, the Internet is alive and well to this day, so his prediction was wrong.
During a keynote speech in 1997, Metcalfe took a copy of the column in which he made the prediction, put it in a blender with some liquid and drank the pulpy mass! This was after he had already tried to eat his words in a form of a very large cake, but the audience protested.