The unlucky recipients of Procrustes’ hospitality were merely stretched or squeezed to fit his iron bed. The denizens of Judd Apatow’s “Funny People” have been pulled every which way to fit a misshapen concept, yet they remain painfully unfunny, and consistently off-putting.

This is Mr. Apatow’s third feature as writer-director. (He has produced and/or written more than a dozen others, many of them hits.) Two years ago he made “Knocked Up,” a lusty and improbably affecting comedy starring Seth Rogen and Katherine Heigl. In 2005 he directed the endearingly hilarious “The 40-Year-Old Virgin” from a script that he wrote with the film’s star, Steve Carell. “Funny People” was conceived as something more ambitious, a comedy about aging and mortality. Adam Sandler is George Simmons, a famous comic who learns he has a life-threatening illness. Mr. Rogen co-stars as Ira Wright, a deli counterman and aspiring stand-up who is hired by George to write jokes, then becomes the older man’s opening act and confidant.

Maybe George hires Ira because he’s so depressed by his medical news that he thinks Ira is funny, though he is not. Maybe the point of Ira’s unfunniness, and all the unfunniness to come, is that comics are lonely, desperate people (George certainly fills the bill), or that the state of contemporary stand-up is lamentable—a point that the movie drives home, whether intentionally or not, with a succession of comedy scenes distinguished only by the repetitiveness and impoverishment of their scatology.

Still, the failures of “Funny People” go far beyond funny or un. Mr. Apatow doesn’t seem to know what to make of George, or how to keep us involved as he journeys through the depths of despair (which aren’t all that deep) toward the stirrings (though we’re negligibly stirred) of hope. It’s not a good sign that the most interesting stage in George’s crabwise development recalls the monstrosity of Lonesome Rhodes in “A Face in the Crowd.” A conventionally happy ending was clearly not in the cards, but the film falls into a sourness that’s barely relieved by Ira’s coming of age in a rambling subplot that, of necessity, becomes the plot.

Mr. Sandler’s presence proves a mixed blessing. He does bring his own celebrity to the production, but his part isn’t one he can submerge himself in, as he did in Paul Thomas Anderson’s “Punch-Drunk Love,” so he cruises through the film without much energy or conviction; even George’s rages come off as perfunctory. Mr. Rogen is often adrift in a role that short-circuits the actor’s vast capacity for exuberance. The cast includes Leslie Mann, who’s effortfully but genuinely charming as George’s ex-girlfriend: Eric Bana is her Aussie husband. The running time is 146 minutes, and that’s no joke.