I once was mad at my friend so I secretly put a letter in both his parents' mailboxes. In the letter, I outed him and thoroughly described the sexual experiences he had, told them he was addicted to cigarettes and smoked a ton of weed with money they give him, exposed how he treated adults in the administration, etc. We're still friends to this day and he has no idea what I've done. In fact, he hasn't even spoken with his parents about his sexuality or habits but 100% knows that they know just from association.
