Pluto being downgraded, Vioxx being taken off the market, another element added to the Periodic Table, global warming, overcrowding, Thalidomide the wonder drug, bacon is bad for you, eggs are bad for you, Olean, bacon is good for you, eggs are good for you, air doesn't have mass, Phlogiston, spontaneous generation, evolution, the Challenger will soon be in orbit, red M&Ms are harmful if eaten, the earth will run out of resources by 2000, the earth will run out of resources by 2010, the earth will run out of resources by 2020, 2030, 2040, 2050, etc., Harmonic Convergence and syzygy in 1988 will rip the planet apart, the Hong Kong flu, Y2K, the Cold War, the Doomsday Clock reads 11:55, the Doomsday Clock reads 11:50, the Doomsday Clock reads 11:59, 11:45, etc., Rock Hudson just has the flu, Mesotheiloma, the Speed of Light is 186,282 mps, 175,000 mps, 192,000 mps., etc., abortion is removal of "unwanted tissue", Solid State, pregnant universe, Nebraska Man, Lucy, SETI, the superconducting semicollider, Archaeopteryx, acceleration to 30 m.p.h. will kill you, flat earth, geocentrism, alchemy, different weights fall at different speeds, etc.
Just off the top of my head ---