I was teaching a very basic class in BASIC programming to a group of adults. Adults who have never been around computers before are very nervous and much harder to teach than children, however I am a patient person so I enjoy their successes.
However, I must share the following:

After putting a short program on the board, I told the students to type “R,” “U,” “N” and press return to see the program execute. A hand went up in the back of the room, waving to get my attention, and the person attached to the hand said, “I did what you said and it didn’t work.” Knowing full-well that all of us make mistakes when typing at the computer, I suggested she retype “R,” “U,” “N” and press return. A few seconds later, the lady’s hand goes up again. “It still doesn’t work,” she said.

So… I went back to see what the problem was … only to find that instead of typing RUN, she had typed in the following: ARE YOU IN!