Aunt Flo is always an unwelcome visitor

Guys of all ages can be kind of clueless about women's bodies. I know a guy who thought women could hold in their period blood as one holds in their pee. It's not necessarily men's fault when they know so little; Sex education programs have been cut for decades, and even when men start getting with women, a lot of basic information can simply slip under the cracks. However, one would think by the time a guy is married, he would be a bit more knowledgeable about the female anatomy. Unfortunately…

How??