Calvin's Sandwiches

Calvin's Sandwiches are very specific(as shown in the picture). The sandwich has to be like this:
 * 1.Chunky peanut butter only.
 * 2.Open faced.
 * 3.No jelly of any kind.
 * 4. Normal bread, no "weird" grain breads.
 * 5. Cut it diagonally.

The humor comes from this strip because Calvin's Mom did exactly all the things she wasn't supposed to.