“Last year, I had a girl who wrote to me every day,” recalled Monica Inzer, Hamilton’s dean of admissions. “She’d send me e-mails; she’d send me letters; she had alums write to me. We all knew that this girl wanted us more than anyone else.”

When a total of three spots in the freshman class opened up, that eager young woman was the first person Ms. Inzer called. “She said, ‘Eh, I’m going someplace else.’ ”

Another applicant eagerly informed Ann Fleming Brown, the director of admissions at Union College, in Schenectady, N.Y., that the college was her first choice — or had become that when her true first choice, Bowdoin, rejected her. It is just one of the many ways, Ms. Brown and her colleagues at other schools say, that students on the waiting list have shot themselves in the foot in recent years.

They have insulted the college’s judgment or taste. They have disparaged classmates who already got in. They have threatened to go over the admissions officer’s head. Showing up and demanding an interview is inadvisable. Showing up with a camping tent, even more so.

And parents are often part of the problem. “There’s a mother who e-mails me every third day — they must have timers on these things,” Ms. Brown said. “There’s one parent who calls up and yells at me: ‘I can’t believe this happened! This is a horrible thing!’ And then he calls 10 minutes later and says, ‘I’m sorry.’ Then he calls and says, ‘I know you don’t like me. I’m being a complete pest.’ ”

To cut down on behavior like that, says David Borus, dean of admissions at Vassar College, “We are very explicit in the communications we send out about what’s going to help you and what’s not going to help you, and we make it pretty clear that if you do do some of this stuff, you’re just going to tick us off.”