How much is your fella riding? It happens, but usually in guys who ride extreme distances/hours. Bike fit, seat position, riding position, and overall health (weight, blood pressure, prostate status, smoking) also matter.

It seems to me like the immediate concern would be how to shut up your friend's husband, as such comments are extremely rude and uncalled for, especially by someone who apparently does not ride, cares not for the sport, and does not have any facts to back up his claim.

If being polite does not work, you could ask him what kind of riding caused his impotence. That ought to make him think twice about bringing up the topic again.