Mab is angry with upper class ladies because their breaths are tainted by sweetmeats (desserts), which was not a pleasant smell. During Shakespeare’s time, sugar began being imported in large quantities from the Caribbean, and its consumption became a status symbol among the rich who could afford it.  Today we know that sugar is the main cause of tooth decay, but in an era before dental hygiene existed, sugar had a truly devastating effect, causing the teeth of the upper classes to rot and smell awful.