What is an example of pseudoscientific idea?

There are a great many pseudo-scientific ideas that are circulating in our world. Immanuel Velikovsky wrote a book called "Worlds In Collision" in which he worked out in great detail how the planet Venus had been ejected from the planet Jupiter, of which it had once (supposedly) been a part, and how by passing close by the Earth, Venus caused various anomalous events which had been reported in The Bible as miracles, such as the rain of manna in the desert, during the exodus from Egypt (supposedly, the Venusian atmosphere reacted with the Earth's atmosphere to produce manna). Nothing in this book has the slightest scientific validity or plausibility, yet it is all presented in the guise of a scientific theory, claiming to be scientific. Hence, it is pseudoscience.