The general premise of the book is that women marry a man they think is Mr. Right, but as time passes he seems to be more Wrong than Right.
This occurs because today's nice modern man attempts to create an "equal" relationship, acting in a way that causes his wife to become more masculine, forcing her to wear the pants.
The book describes how this happens and offers a remarkable simple solution that is based on a skillset any man can learn.
An image that conveys the ideal man with an obvious flaw (dragon tail or head) could work, but that is just one possible direction.
Another direction might be more along the lines of pure graphic elements, not using a human figure but something that conveys the contrast between Mr. Right vs Mr. Wrong; good match vs. bad match; change from right to wrong over time; etc. (see the "What we want vs. What we don't want in the content details above.