‘Run, Fatboy, Run’: Flat-footed comedy stumbles

The best thing about “Run, Fatboy, Run” is its title, but even that is in doubt.

Are there commas in the title? Is Fatboy one word or two? Finding a definitive answer to these questions is difficult, but then a lot of movies are like that now. (Check out the variations on the first “X-Men” sequel.)

I have just been handed a note saying the correct title does not have commas. But I remain suspicious.

Anyway. “Run, Fatboy, Run” joins the roster of comedies about Peter Pan males who are forced to grow up and enter the adult world.

In its prologue, the movie introduces us to Dennis (Simon Pegg, from “Shaun of the Dead”), a terrified London groom. On his wedding day, he flees from his pregnant fiance Libby (Thandie Newton, late of “Norbit”).

Five years later, Dennis is an overweight, chain-smoking layabout. (Trim Simon Pegg adopts a none-too-convincing belly pad.) He works as a security guard in a department store and sees his young son when he can.

Libby has taken up with a go-getting American (Hank Azaria), a relationship that runs into a familiar movie problem: When your villain is this vile, it reflects badly on the person involved with him. Libby would have to be an idiot to hang around with this guy, yet the movie insists she’s not an idiot.

Dennis gets the mad idea that he will win Libby back by participating in the London Marathon. He has never followed through on anything in his life, so this is his chance to prove his commitment — to something, anything.

As forced as this plot might be, it still has possibilities. Which leaves me curious about why this movie didn’t make me laugh.

I found almost everything stilted and unfunny, despite the presence of expert comic performers such as Pegg and Azaria. The only exception is Dennis’ best friend, a man even more irresponsible than Dennis. Irish comedian Dylan Moran is splendid in the role (he got eaten alive in “Shaun of the Dead”).

The script is by talented Michael Ian Black, a member of the comedy groups The State and Stella, with a rewrite by Pegg himself; it’s directed by David Schwimmer, the “Friends” star.

Maybe it’s the translation between American and British humor, or maybe it’s just the timing. With comedy, every comma must be exactly in place. Even in the title.