Some of them I didn't experience first-hand, but rather heard about.
My younger brother, told me about these two.
In a fourth level English class:
"Why is the e upside-down in the definition?"
"Is 'would like' one word?"
My friend Taylor told me about this one:
Typical dumb blond raises hand during debate. "I read a book once..."
Yes, that was the end of her statement.
My friend Jade told me about this one, after watching a video on the Panama canal.
A girl raises hand. "I don't get it... If the water-level raises, wouldn't the ships eventually sink?"
My friend Rachel told me about these three.
During her Freshman year: "What's the number for 911?"
"Have we ever had a black president before?"
"Are we still at war with Iraq?"
And my personal favorite, was during my favorite English class of all time. Not so much a dumb question as a rather unsettling one. Then again if you're not a lover of literature as I am, it won't seem so bad.
"Why do we have to read these books by dead authors about shit that never happened, or happened way before we were born?"
Needless to say, two other people and myself went off on a huge tangent about why classic literature is important. Afterward, she replied, "Okay. That makes sense."

Lesson well-learned.