"IT SEEMED LIKE A GOOD IDEA AT THE TIME"

I really only have one item for this list, so please add your own.
  1. Bacon (and other savory) chewing gum.
  2. That's all I've got. Add your thing. Or don't.
  3. McDonald's
    Suggested by   @biz
  4. Habañero pepper hot sauce
    I was like, "I'm super cool and I can handle anything!" And then no.
    Suggested by   @bredee
  5. New Coke (and pulling "classic" Coke from production.)
    Suggested by   @RichardGoodman