Definitely not a bicycle built for two
Danger, and from an unexpected source. Men, you may want to leave the room now, especially if you are the sensitive sort.
Today's NY Times has an article on the hazards of bike-riding--yes, you heard me, bike riding, specifically the bicycle seat. And don't think you'll avoid the problem by using one of those new-fangled ergonomically blah-blah-blah seats, either. No; they appear to be, if anything, worse.
Since the Times is registration-only, I'll give an excerpt--a rather expurgated excerpt. Read the whole thing for the precise anatomical details--if you dare.
The studies add to earlier evidence that traditional bicycle saddles, the kind with a narrow rear and pointy nose, play a role in sexual impotence.
Some saddle designs are more damaging than others, scientists say. But even so-called ergonomic seats, to protect the sex organs, can be harmful, the research finds. The dozen or so studies, from peer-reviewed journals, are summarized in three articles in September's Journal of Sexual Medicine...
Researchers have estimated that 5 percent of men who ride bikes intensively have developed severe to moderate erectile dysfunction as a result. But some experts believe that the numbers may be much higher because many men are too embarrassed to talk about it or fail to associate cycling with their problems in the bedroom.
The link between bicycle saddles and impotence first received public attention in 1997 when a Boston urologist, Dr. Irwin Goldstein, who had studied the problem, asserted that "there are only two kinds of male cyclists - those who are impotent and those who will be impotent."
Although Bostonians (and even Boston neurologists, as far as I know) are not ordinarily given to hyperbole, the evidence is that Dr. Goldstein was over-the-top on this one. But 5% is nothing to sneeze at, either. So, forewarned is forearmed, all you bicycle-riding guys out there.