Killjoy was here

U., the narrator of Mike Albo's new novel ''The Underminer," is a psychological predator of the highest order. A viper cloaked in velvet. The Shaquille O'Neal of schadenfreude.

She is the type of ''best friend" (her phrase) who keeps you posted on the romantic exploits of your ex-boyfriend from college and the phenomenal music career your ex-bandmate is enjoying now that he's gone solo. In her mouth, the milk of human kindness turns into sour cream.

U.'s successes -- a best-selling children's book, windfall investments, foundation grants and gallery shows, A-list Manhattan parties and celebrity pals -- come as easily to her as anxiety attacks and weight problems do to you. The more you struggle with bloating and depression, the more dependably she'll be there with a sympathetic smile and a comment on the order of, ''People get too hung up on thinness. You're more like a typical American."

The subtitle to Albo's novel, written with Virginia Heffernan, neatly bumper-stickers the archetype: ''The Best Friend Who Casually Destroys Your Life."

While not from precisely the same charm school, Debbie Downer, a recurrent character on ''Saturday Night Live," has a similar effect on the unfortunates around her. Played by cast member Rachel Dratch, the aptly named Downer is the sort who goes on family vacation to Disneyland and, over breakfast, brings up mad cow disease and terrorist attacks. She's ''always there to tell you about a new disease, a car accident, or killer bees" goes the skit's catchy musical intro. TV Guide called her ''last season's breakout character."

In real life, you'd break out in hives just sitting next to her.

Coincidence or pop-culture trend? That's hard to judge, because writers, comedians, filmmakers, and other artists have been inviting skunks to their garden parties for as long as there have been skunks and garden parties.

Woody Allen's film oeuvre alone offers enough underminer and downer types to populate a small cruise ship. But at least one observer who's encountered The Underminer both in book form and in one of Albo's monologues traces U.'s lineage back a couple of millennia before Woody. In a column posted on the Jewish World Review website, writer-critic Ron Rosenbaum calls The Underminer ''a defining figure for our age, alas," and cites the Greek writer Theophrastus as one artist who caught on to these urban-predator types long ago.

Even in ancient Greece, writes Rosenbaum, there were ''obnoxious talkers who define themselves and derive much of their irritation factor from their annoying, dishonest, hostile or hypocritical tone of voice." He concludes, ''There must have been a lot of captious yammering in Athens, along with the noble orations."

Still, the sharpness and hilarity with which Albo and SNL draw their characters suggest that one path to creative pay dirt these days is lined with wet blankets and reservoirs of passive aggression.

Consider:

''Sideways," which is up for a best picture Oscar this weekend, features a pair of characters who are paradigms of the life-ruiner and mood-destroyer. On a buddy trip through California wine country, Miles (played by Paul Giamatti) uncorks his well-ripened depression and pours it liberally over Jack (Thomas Haden Church), his friend from college, who is looking for some premarital hanky-panky, not prenuptial soul-searching.

Jack, meanwhile, puts Miles in one impossible situation after another with his incorrigible lechery and colossal obtuseness. The comedy in their pairing -- and there is plenty -- lies in the way these two torture each other without trashing a friendship that appears to be built more on loyalty and longevity than logic.

Redbook magazine published a recent feature titled ''Toxic Friends," in which two of the seven types identified in the story are -- hello -- The Underminer (''She chips away at you with subtle, delicate strokes") and The Downer (''. . . you may be tending to her perpetual angst as an excuse to keep dodging your own problems and challenges").

Much of the material was adapted from Jane Greer's book ''How Could You Do This To Me?" Greer, a Manhattan psychotherapist and Redbook contributor, is not surprised these types are popping up in pop culture as well as in real life, especially in upscale urban settings.

''They've always been with us," says Greer. ''But it's intensified as the culture has become more cutthroat, and more competitive. As a result, there's been more need to conceptualize these types, too."

An episode from season three of HBO's hit series ''Sex and the City" gave birth to the term ''frenemies" to describe erstwhile friends who are anything but. In the episode, Charlotte (played by Kristin Davis), whose husband has been experiencing erectile dysfunction, confesses her marital frustration to a group of college pals -- and is cold-shouldered into a humiliated silence for her candor. Samantha (Kim Cattrall), meanwhile, whose sexual exploits have been driving her friend Charlotte up a wall, finds a new friend who is far more libidinally liberated than she -- and discovers to her embarrassment that even liberation has its limits.

Near the end of ''The Incredibles," another of the year's hit movies, an insidious, subterranean archvillain pops up and threatens to wreak havoc on the family of superheroes. His name? The Underminer.

Albo, a comic monologuist and author of one previous novel (''Hornito"), says he got the idea for ''The Underminer" four years ago when Heffernan, his former roommate, reported a friend had said ''the most undermining thing" to her. A light bulb went off, and a character was born -- although Albo never specified U.'s gender (the inference is easily drawn that U. is female) and other characteristics in his novel.

''Once I started, both in performing and in my own life, I noticed this character was more ancient than I'd thought," Albo says in a telephone interview.

Not only in New York but in cities like Los Angeles and San Francisco, he says, audiences have responded to The Underminer with knowing looks and nods. Any city, in fact, with a young, upwardly mobile population is likely to be fertile territory for The Underminer, he says, whose modus operandi is the seemingly supportive comment that cuts to the core. ''It's like the friend who says, 'Oh, your little son looks so cute playing there alone in the sandbox. He doesn't even seem to mind that you're not there,' " quips Albo.

Stumbling upon other manifestations of The Underminer in Redbook and ''The Incredibles" was weird, adds Albo. ''We seem to have tapped into this cultural whisper that's going on right now."

In real life, counsels Greer, the strategy for dealing with a downer or underminer -- defined by her as a ''narcissistic personality who presents as looking out for you, but who're really out for themselves" -- depends on how much the friendship is worth.

''If you truly value the relationship, it makes sense to address the behavior and focus on the future," says Greer. But if the behavior does not change, she adds, ''Then it's a question of being able to move on."

Or, if you're seated at the breakfast table with Debbie Downer, at least move over.

Joseph P. Kahn can be reached at jkahn@globe.com.