Speaking of "feeling bad for teaching someone"... I must have been in 5th grade and this other kid was talking about shorting out a power outlet. I said "What I'd do is unfold a couple of paperclips, stick them into a rubber eraser, then plug that into the outlet and twist it to get the paperclips to touch."

A few days later the principal calls me in. "Did you tell him to do this?" "I didn't tell him to, we were just talking about how to do it." "... well, he's done it before. Don't do anything like this again. Dismissed." I still can't believe that I got out of it; petty tyrants love to flex their power.