What was the best prank that you pulled?

When I was 13, I invited a new friend (we'll call her Liz) to swim in my family's pool after school. I have a sister 2 years younger than me, and I warned my friend that my little sister was mentally handicapped, and that she'd get startled easily by strangers so she had to speak quietly and make no sudden movements to avoid my sister having an "episode". Of course, my sister is a normal functioning person, but Liz was very sweet and gentle with her. After they met, my sister asked me in private if everything was okay because Liz was acting strange and whispering at her. I told my sister that Liz was mentally handicapped and to be really careful around her because sudden movements and loud noises scared her. My sister started being very careful around Liz (whispering, talking slowly, etc.), and they both went on thinking that the other was special needs until Liz spoke with another friend of mine weeks later about my "special sister".

Edit: Thank you for the gold! Reddit likes something I did over a decade ago!? I feel so validated XD

/r/AskReddit Thread