NEW YORK — This summer, hide your bridesmaids. So warns the promo for this weekend's new movie, "Wedding Crashers", which is about a couple of bachelors who show up at weddings uninvited to prey on lonely bridesmaids and especially desperate female guests. The movie cashes in on two common stereotypes about weddings: that women hate attending nuptials alone, and that men, realizing how vulnerable weddings make single women feel, use the occasions to their advantage. But how are true are these generalizations?