MY teenage son recently informed me that there is an Internet quiz to test oneself for narcissism. His friend had just taken it. “How did it turn out?” I asked. “He says he did great!” my son responded. “He got the maximum score!”

When I was a child, no one outside the mental health profession talked about narcissism; people were more concerned with inadequate self-esteem, which at the time was believed to lurk behind nearly every difficulty. Like so many excesses of the 1970s, the self-love cult spun out of control and is now rampaging through our culture like Godzilla through Tokyo.

A 2010 study in the journal Social Psychological and Personality Science found that the percentage of college students exhibiting narcissistic personality traits, based on their scores on the Narcissistic Personality Inventory, a widely used diagnostic test, has increased by more than half since the early 1980s, to 30 percent. In their book “Narcissism Epidemic,” the psychology professors Jean M. Twenge and W. Keith Campbell show that narcissism has increased as quickly as obesity has since the 1980s. Even our egos are getting fat.

It has even infected our political debate. Donald Trump? “Remarkably narcissistic,” the developmental psychologist Howard Gardner told Vanity Fair magazine. I can’t say whether Mr. Trump is or isn’t a narcissist. But I do dispute the assertion that if he is, it is somehow remarkable.