I was about eleven or twelve, and I shared a room with my sister, who is six years younger than I am. I am the oldest sibling; my sister is the youngest sibling - we never talked; everything was a quarrel.
One of our recurring fights had to do with keeping our room clean. I, being the older, was blamed if the room didn't meet my parents' standards, which meant that I often had to clean up after my sister, as well. I got tired of my sister's clothes and toys being on the floor pretty quickly.
So one day, my mother went out to run some errands, telling us that our room better be clean by the time she returned home. My sister proceeded to sit down on the floor and watch me clean. I picked up my clothes, yelling at her to do the same; I picked up my books, yelling at her to do the same; she sat in her position on the floor and said: "I am!," though she clearly wasn't.
The year before I had read "Little Women," and I remembered Beth's death scene well. So I put on my "sick voice," you know, the one you use to get out of school but your mother doesn't tend to believe, and I told my sister that I wasn't feeling too well. I asked her to please help me clean, because I had scarlet fever and I was dying. I continued the story, saying that there wasn't a cure, so I was definitely going to die - and that, because there was no cure, I hadn't told our parents about my illness, because it would just make them sad. Therefore, she should help me clean and not tell our parents about my illness.
Turned out, my sister had a heart (who knew?). She told me to lie down on the bed, asked if I needed anything to eat or drink, and proceeded to clean.
Of course, when my mother came through the door, my sister ran to her crying because I was dying. Luckily, my mother had to struggle too hard not to laugh, so I didn't get more than a scolding.
It was kind of mean, and it probably only worked because my sister was only 5 or 6, but it's a pretty hard con to beat.