* "Isn't k'vayachol one of God's name?" The word means something like as if it was possible and is often used as follows: "God (k'vayachol) said to Moshe..." Thus, the mistake.
* "How does the ibn Ezra learn Rashi?" Rashi was a very close reader who used Midrashim to explain textual anamolies. The ibn Ezra read more broadly, and rejected many midrashim because he found them irrational or illogical. When Rashi cites a midrash the ibn Ezra has debunked heads explode among those who don't remember that (a) Rishonim are allowed to argue with one another;
* "The fact that every Jew in the world today believes in matan Torah proves it happened." Every Jew? In the world? Don't you mean only the Jews you choose to recognize? Anyway, about 2-billion people (more if you count the propreiter. of Cross Currents) think Jesus was God's son. Does that argument satisfy you? Or is it proof of a mass delusion and nothing else? Lots of crazy ideas have been accepted over the centuries. Celts believed in fairies. Irishmen believed in Leprechauns. Polish fat women believed in demons, ghosts and witches. How did these ideas become, for a time, so widly accepted? The most we can say, citing the writings of Josphous and his coeivals, is that some people living around the year zero thought their ancestors had experienced a revelation. What does that tell us about the other Jews living at that time. Nothing. What does it tell us about their ancestors? Also nothing. Though you can prove to a disinterested party's satisfaction that some Jews living around the year zero had embraced a mighty strange idea it doesn't follow that the strange idea is true.
UPDATE: Almost forgot the best one: "George W. Bush is Israel's BEST FRIEND EVER! EVER!" I still can't beleive that stunner was repeated by educated men.