For example, a friend of mine is an avid mountain biker. She (that's right, I have a few) was set up with a guy on a weekend of trail riding with two other couples. The new guy, let's call him "Lance," shows up with a spanking new bike, looking like a world of opportunity.

So off our sextet goes into the wilderness. Pedals are pushed and stumps are jumped until Lance takes a small digger. Almost as soon as he's down, he's back up, berating his bicycle. He kicks it, and refuses to pick it up. His date carries it miles back to the car. Then he demands (through choked-back tears, I can only imagine) to be taken to get his hand checked out.

After kicking his mean ol' bike, and taking the group away from their fun, it turns out that his tantrum was justified, after all, because he had broken his pinky. A pinky? Are you kidding me? For the nuts on top of this head-case sundae, when they got back to the hotel, he still wanted to sleep with my friend. If only he'd had such balls when he fell off his bike.

Even in the best-case scenario, when skill levels are roughly equal, the sports themselves often are not: five-setters vs. three-setters, ladies' golf tees, women's basketballs ... softball. Men and women don't play the same games, which should tell you all you need to know.

Sports can be a bonding experience. Watching sports is a great way to pass a few hours together without having to pay any attention whatsoever to "togetherness." But even with both teammates playing at their selfless best, relationships are a three-legged race run over a mine-filled obstacle course while wearing flint-rock corduroys soaked in gasoline. In a word: volatile. The last thing you need to bring along is a blowtorch. One bad tennis match, and BOOM!, the rackets go flying—and so do the championship rings.