When I was about 7, tricked my younger brothers into using "the C word" (you know which one), by telling them that it was a word used to describe any non-specific item. My mum was less than impressed (with them, she had no idea of my involvement).
Oh yeah, and when I was about 5 or 6 I tricked my youngest brother (then 3 or 4) into flipping my dad the bird by telling him that it was a greeting and was akin to just waving at someone. Needless to say that my dad wasn't happy with my brother, and i'm pretty sure my brother was smacked as a result of that.