Because he'll just buy a bunch of trash.
  1. When he's angry.
    Like tonight, when the Packers lost badly and we stopped to get bread and he grabbed two half-gallons of Publix Premium ice cream and a bag of Halloween candy.
  2. When he's not hungry.
    Like if we eat a big lunch or something, and then try to plan for dinner. If he's not hungry, he cant even think about actual food, he just thinks about what junk food he'll want to eat in an hour or so. It's bad. Every suggestion I make for dinner gets shot down while he picks up some cookies or whatever.
  3. When he's hungry.
    Keep him away from the damned store in this situation. Once when I was sick, I sent him to the store for a few things to make some soup. The guy came back with so much chocolate, that the cashier made a joke about being high and having the munchies (because there's no other rational explanation!).