Facebook one I'm afraid. Acquaintance advertising for people to sign up to her 'book exchange' scheme. You send 1 book and get 36 in return. I replied saying isn't this just a pyramid scheme, and people at the bottom won't get anything? (It works by everyone signing 6 people up, and you give a book to someone 2 steps up. So by the time you have 11 levels you are up to 60 million people needed....)
She got really shirty with me, telling me to mind my own business if I wasn't interested and not be so negative. I probably should have kept out of it, but she's normally an intelligent enough person and I'm pretty sure wouldn't want to rip anyone off, so put it down to her not really understanding.
(And yes, I am definitely being unreasonable for starting a fb thread).