Bad (A1)

He was a bad friend.

Horrible (A2)

Today was a horrible day: I got low grades in three subject.

Terrible (A2)

That story has a terrible ending: the main character dies in a car accident.

Awful (B1)

I have never eaten such an awful pie.

Dreadful (B2)

Although the weather was dreadful, they were determined to go on a trip.

Appauling (C1)

In spite of global weather changes all over the world, humanity is not able to see the appalling consequences of eccessive use of cars in metropolitan cities.