Hookups may be fine for college students, but what about after, when they start to build an adult life? The problem is that “young people today don’t know how to get out of hookup culture,” Ms. Freitas said. In interviews with students, many graduating seniors did not know the first thing about the basic mechanics of a traditional date. “They’re wondering, ‘If you like someone, how would you walk up to them? What would you say? What words would you use?’ ” Ms. Freitas said.

That may explain why “dates” among 20-somethings resemble college hookups, only without the dorms. Lindsay, a 25-year-old online marketing manager in Manhattan, recalled a recent non-date that had all the elegance of a keg stand (her last name is not used here to avoid professional embarrassment)…

“I’ve seen men put more effort into finding a movie to watch on Netflix Instant than composing a coherent message to ask a woman out,” said Anna Goldfarb, 34, an author and blogger in Moorestown, N.J. A typical, annoying query is the last-minute: “Is anything fun going on tonight?” More annoying still are the men who simply ping, “Hey” or “ ’sup.”