Hint: If he never wants to go out ...

And you only see him on certain nights of the week, he's probably up to no good.

Don't Date Him Girl provides a searchable database of bad dates. So does Manhaters.com. Women post about the bad apples they've dated so that others can learn from their experiences.

As for Vincent of Jacksonville, his ex said she answered a knock at her door one day only to find his wife and his mistress had come calling. The two, having found out about each other, "don't mind teaming up to get rid of the next girl," the ex-girlfriend said in her posting. "Whatever you do, don't date him, don't speak, just move on."

And Michael, the 23-year-old from England? "He only cares about himself and how many notches there are on his bedpost," reported one of the women he counted as a notch. "Ultimately, he'll end up sad and lonely. Probably with a hefty bout of gonorrhea."

I'll admit that I searched for former flames, but got no hits. Nor do I plan to contribute to the database. Others, however, feel it's their duty to expose the men who done them wrong.

Andrea Wells of New York City heard about DontDateHimGirl.com from a friend a few months ago and signed up. She knew just the guy to expose, a handsome, charming would-be rapper named Serge. The two met at a concert a year ago and dated for five months, she said. She went to his house just once and thought the place looked overly spare. There were few clothes in the closet, for example.

Their relationship ended abruptly when Serge's disconsolate wife sent Ms. Wells a message from Serge's BlackBerry, alerting her that Serge was married. Thinking back to her visit to his house, Ms. Wells realizes "he hid everything — wedding pictures, shampoo."

"I posted his story," she said. "It's public knowledge. Everyone should know. A marriage license is public knowledge."

And while she acknowledges that every story has two sides, "It's a perfectly good thing for women to check," Ms. Wells said. "At least it gives you a heads up."

Another resource is TrueDater.com, which allows users of online dating sites to see whether their chosen date matches his or her profile. You can browse the site here.

Isn't it romantic?