(I was the subject of a few strange looks when taking this photo in the toilets at Sainsbury's. But I am committed to bringing you updates on the unhelpful perpetuation of these aspects of sexual culture.)
This one seems to be aimed at those who have a "she" partner. Will it not work otherwise? I was unable to find an explanation for this in my research.
See also "Normal Healthy Men Of The World - Your Penises Still Aren't Good Enough"
and "Men & Sexual Myths - Two Steps Forward, One Step Back"