Tamagotchi
"I had a Tamagotchi, but I got bored with it, and I forgot to feed it, and it died." That right there? That is the story of every single person who ever bought one of these things (or received one as a gift). I know at least four people off the top of my head who had that exact same experience. In fact, the Tamagotchi was perfectly designed for the user to get bored with it, forget to feed it, and eventually kill it.