Good carbohydrates break down into glucose, which translates into energy. They can also provide fiber, which helps you feel full and keeps you regular (if you know what I mean). Bad carbs are like those nameless but well-dressed people at awards shows that sit in a celebrity's seat when they get up to present or pee. They're filler people, and bad carbs are filler foods. They're good in the moment, but not necessary in the long run.
To clarify, I present the following infographic:
Question: What's your favorite good carb? Bad carb? (You know you have one...) Me, I dig apples and crusty whole grain bread. And cupcakes. If I could only learn to refuse the cupcake.