A word pioneered by my father, Michael. Pizza titties are a pair of woman's breasts that when they have grown to outrageous proportion as to project out from the chest over a foot in length you may rest a pizza on them. In basic terms, titties so big that You could successfully place a pizza on them without the pizza falling off and proceed to eat the entire pizza.

When you're being horny (especially around friends) and as a result shame ensues.