Simon Pegg is lovable loser Dennis, a classic commitment-phobe who walks out on heavily pregnant fiancé Libby (Thandie Newton) on their wedding day.
Five years later Dennis is pulling dead-end hours as a security guard and sleeping in a seedy North London basement apartment. Libby has moved on to bigger and better things, most notably rich and handsome financier Whit (Hank Azaria).
Tired of being a nearly-man and determined to impress Libby and their son Jake, Dennis vows to run in the same 26-mile charity marathon for which Whit is training obsessively. Feel the burn!
Naturally Dennis is hopelessly unfit (though not exactly the fatboy the title suggests) and seemingly incapable of completing even the simplest of menial tasks. Altogether trite but true to the kind of comic roots that include the timeless workout montage, clash of the male egos, and heartstring-tugging finish line drama.
Not a surprise in sight, just predictable losers-are-people-too jesting raised a notch by the quality work of consummate professionals who are better than their mediocre material.
Pegg and Azaria come closest to generating real laughs, their macho posturing the source of some genuine wit. Newton lends class where it's desperately needed; beauty and the beast et al. Pop tune soundtrack is effervescent and feel-good finale ends on a rose-colored note.