We don't know what possessed the chap to pee on a pregnancy stick in the first place - but it's a stroke of luck he did, as when the sign came up pregnant, the shock was enough to send a friend of his online looking for answers.
CappnPoopDeck posted a rage comic of his friend's experience on social news site Reddit, complete with a sketch of a horrified male face confronted with an unwanted - and biologically impossible - pregnancy.
The very first commenter on the story, which has now been viewed over a million times, gave some concerned medical advice: "If this is true, you should check yourself for testicular cancer. Seriously. Google it.”
Thanks to this internet sage, CappnPoopDeck's friend did do the checks - and found he had indeed contracted cancer.
So what's going on here? It turns out that men suffering from choriocarcinoma, a rare form of testicular cancer, produce a pregnancy hormone (HCG) that is also found in the female placenta.
But before you go and widdle all over your girlfriend's pregnancy test, be advised: less than 1% of testicular cancer cases show up through this gender-bending test.