Left image: Three happy people with heads full of hair standing behind a sad person with no hair.
Right image: Three sad people wearing swimming caps standing behind a happy person with no hair in a swimming pool.
The image is ironical, as person without hair is sad in a normal situation due to the absence of hair, unlike other people with hair. However, in a swimming pool, people with hair have to wear swimming caps, which is uncomfortable, while the person without hair does not need a cap, and is thus, happy in this situation.