For each shape, take a moment to discuss or reflect on how it fails to meet the definition of "regular." For example, in the quadrilateral on the left, all the sides have the same length. But because the angles are not all the same, it is not a regular polygon. In the rectangle, all the angles are the same, but the sides have different lengths. So it is not a regular polygon.
This is best done as a full-group discussion with an overhead or at the board. Have someone draw the two regions, hold up cutouts of the shapes, and ask the group to decide where each would go. If you are working on an overhead, string is better for creating the regions than drawing because it is easily altered to "fix" the regions to overlap.