It's literally impossible to tell when and how often a period will strike.

From the Hammerkatz sketch team at NYU comes this very, um, educational new video, entitled "Tampon Commercial - Presented By Men." If dudes were ever to use their usual trusty combo of overwhelming confidence and impenetrable obliviousness in a tampon commercial writers' room, the result women might get stuck with would look something like this:

Thank goodness dudes get grossed out so easily. Not me, though. I'm never too shy to go to the store to get my wife some egg-scooper-uppers-and-putter-back-inners when she's on her thing. The thing that is her period.

Sources: Hammerkatz NYU