Date the Girl You Think You Can't Have – Part 1

A Friend's Ex

Resist the urge. Date these women at your own risk.

Number who have indulged:25 percent of men, 23 percent of women

Why you want her:Your buddy has extolled her virtues so relentlessly, she's become the woman of your dreams, too. "He's basically given you a sales pitch for his girlfriend," says Amy Bippus, Ph.D., a professor of communication studies at California State University at Long Beach.

What to consider:If the separation wasn't mutual, beware. "There's no bigger blow to a man's self-esteem than to be rejected in favor of a friend," says Judy Kuriansky, Ph.D., author ofThe Complete Idiot's Guide to Dating.

What to do:If you must act, stay away until he has moved on to another love interest. "There's a psychological threshold that's crossed when a person takes up a new relationship," says Kerner. "Plus, you don't want to look like a scavenger."