A tattletale is someone who tells an adult, a teacher, or a person in charge about the small bad things another child did. It is children's language, American English — British children say 'telltale' or 'sneak'. It is an insult, though a small one: the child who is called a tattletale is being told that reporting your friends is worse than whatever they did. Adults use it back to children too ('don't be a tattletale'), and here is the honest problem with it — grown-ups sometimes use the word to silence a child who is reporting something real and serious. That is worth saying out loud to your students. It is also used as an adjective for something that gives a secret away: a tattletale stain, a tattletale grey. Adults rarely use it about other adults; for that, English says 'snitch' or 'informer'.

愛打小報告的人、告狀精（美式，小孩子在用的話；英式說 telltale）