Some misconceptions on this list that I already knew about:
- Sushi does not mean "raw fish", and not all sushi includes raw fish. I actually never ate sushi myself before I became vegetarian (ovo-lacto vegetarian, not pescetarian), and I now enjoy sushi frequently.
- The Great Wall of China is not the only man-made object visible from the Moon. In fact, no Apollo astronauts reported seeing any man-made objects from the moon.
- A person who is drowning does not wave and call for help, as in fictional depictions of drowning. I read about this potentially life-saving information last year, which is especially pertinent to me as I cannot swim.
- It is not nutritionally necessary to combine multiple sources of vegetable protein in a single meal in order to metabolize a "complete" protein in a vegetarian diet. I've corrected people on this misinformation often.
- The Coriolis effect does not determine the direction that water rotates in a bathtub drain or a flushing toilet.
- Bulls are not enraged by the color red, used in capes by professional matadors. They're color-blind; it's the movement that annoys them.
- The historical Buddha was not obese. Depictions of a chubby Buddha are of a future incarnation of the historical Buddha, Siddhartha Gautama, who advocated a middle way between indulgence and abstinence.
- Also, the Buddha is not a god. I learned this information about Buddhism in college, through academic study and personal conversion to the religion (though I don't generally identify as Buddhist now, its ideals are close to my personal philosophy).
Some misconceptions I've never heard of before, which I found interesting or weird:
- The notion that goldfish have a memory of only three seconds is false. Never heard that one.
- Glass is not a high-viscosity liquid at room temperature. It is an amorphous solid.
- In South Korea, it is commonly believed that sleeping in a closed room with an electric fan running can be fatal in the summer. Fan death - entirely new to me.
And some misconceptions I myself had and am now disabused of:
- The human brain can create new neurons after birth. Fascinating.
- John F. Kennedy's words "Ich bin ein Berliner" are standard German for "I am a Berliner", not "I am a jelly donut". My college German teacher gave me this misinformation.
- Lemmings do not engage in mass suicidal dives off cliffs when migrating. This myth originated from the Disney film White Wilderness, and reading about their film crew's mass killing of lemmings for theatrical purposes really pissed me off.
ETA: The revision history and discussion page for this Wikipedia article are abuzz with activity; some of what I list above may already be incorrect or obsolete :-)