Run Fatboy Run

I'm not fat! I'm just... unfit...

Dennis Doyle (Simon Pegg) is a clueless and slightly overweight Man Child who left his pregnant fiancée Libby (Thandie Newton) at the altar five years earlier. He constantly tries to persuade the woman he loves to accept him back into her life, but when he discovers that Libby has found a new partner in the form of American Whit (Hank Azaria), frustration grows, and Dennis vows that for once in his life, he will finish something. This something ends up being the Nike River Run in London. With his friend Gordon (Dylan Moran) and landlord Mr. Goshdashtidar by his side, Dennis begins training for the marathon he must finish to win the respect of both Libby, and himself.

This film provides examples of:

The Ace: Whit; "Peter Perfect" as Dennis calls him.
Actor Allusion: David Walliams' cameo is similar to his Little Britain character who goes into shops asking for oddly specific things.
Added Alliterative Appeal: "Dennis Doyle from downstairs"
Ask a Stupid Question: After explicitly pointing out that Dennis is running on a broken ankle, the reporter then asks:

Reporter: Sir! Sir! How do you feel?

Dennis: (in tears, barely cognizant) How the fuck do you think I feel?!

Blackmail: When Dennis refuses Maya's ultimatum to kick him out if he quits the race and pay his back rent if he doesn't, she whips away his Modesty Towel and takes a polaroid of his naked body. "Deal?" "...Deal."
Cranky Landlord: Played with; Mr. G is a cheerful, forgiving type, but his daughter Maya takes it upon herself to chase Dennis up for the rent.
Cheaters Never Prosper: Whit trips Dennis up, only to be sent to hospital himself while Dennis limps on, and later to get caught out by an action replay.
Consequence Combo: There are a lot of carrots and sticks in play, but the clearest example of the trope is Maya's ultimatum - if Dennis finishes the race, she'll call off his back rent. If he doesn't, she'll kick him out.
Derailing Love Interests: Whit, who starts off The Ace and gets gradually more Control Freaky and competitive in direct contrast to Dennis getting more responsible and mature.
Down to The Last Play: Hugely averted. Whit is taken out of the race very early, and Dennis severely injured, and the rest of the marathon is spent limping in last place, determined to finish. All of which makes Jake's "dad, you won!" utterly heartwarming.
Enforced Method Acting: in the scene where Simon Pegg and Hank Azaria are talking in the locker room, Simon's shocked reaction to Hank dropping his towel was very real. Apparently, Hank was supposed to wear a modesty patch over his genitals, but it didn't fit, so he did the scene without it.
Excited Show Title!
The Family for The Whole Family: A low-rent London Gangster who appears to run a betting syndicate and fence stolen goods, who nearly breaks Gordon's hand in a piano lid, and who when his bet is threatened hijacks a taxi, drives to the race and... runs alongside Dennis taunting him and ineffectually trying to trip him up. Lampshaded after Mr. G rescues Gordon from the piano incident;

Mr. G.: Your friend is man of honour. He promised to beat shit out of you later!

Graceful Loser: Even the Neighbourhood Friendly Gangsters who bet against Dennis are cheering him on when he crosses the finish line.
Groin Attack
Guess Who I'm Marrying
Heart Is Where the Home Is
I Gave My Word: Somewhat justified despite the Honor Before Reason, since his ability to keep a promise is what Dennis is really' trying to prove.
Implacable Man/The Determinator: Dennis, ~~running~~ limping the best part of a marathon on a sprained, implied to be broken ankle because he promised he would, dammit!
Inconvenient Itch: When he first starts working out, Dennis gets a nasty, itchy rash on his crotch that he absolutely has to scratch... as he is at work as a security guard in a lingerie shop. One can guess what this looks like.
I Resemble That Remark: in Libby's bakery;

Libby: You can't even finish your sentence!

Dennis: Oh... don't... don't... don't be... what's the word?

Ironic Echo: "No, but you can watch me do it."
Jerk Jock: Whit.
Kent Brockman News: The overexcitable reporter. "He deliberately tripped him! Bastard! Sorry, got carried away again..."
- "And, what's that? [overjoyed] He's got a son! I didn't know he had a son! Did you know he had a son!?"
Lawyer Friendly Cameo: Dennis and Whit are running in an annual marathon in London on a Sunday, with space for a number of charity runners to enter after the general closing date, that is most definitely not the London Marathon.
Man Child: Dennis's whole problem.
Modesty Towel: Played with twice. Whit drops his in the changing room, giving Dennis an eyeful, and Maya whips Dennis' away after he gets out of the shower in order to take a blackmail photo.
Newscaster Cameo: BBC Breakfast presenter Chris Hollins As Himself, commentating on the race with Denise Lewis.
Noodle Incident: Gordon's one serious relationship somehow ended with "a broken collarbone and a dead meerkat."
Over and Under The Top: Gordon basically exists to make lazy slacker Dennis look almost ambitious in comparison. But comparing him to Whit isn't quite so favourable.
Overly Narrow Superlative: "That's the second most disgusting fluid I've ever had in my eye!"
Pants Free: When Gordon invites Dennis into his apartment, we get a shot of Gordon leaning on the railing from the living room, revealing that he's naked from the waist down. At the end of the movie, he invites two beautiful girls onto his boat... again, no pants.
Parent With New Paramour: Averted at first, Jake is pretty impressed with Whit, which to Dennis just makes him even more depressingly superior. However, they're never as close as he is with his dad, and when Jake really starts going off Whit you know the guy's doomed...
Precision F Strike: Jake on Whit: "what a shithead..."
Product Placement: shamelessly, for the ~~film's~~ marathon's sponsors Nike. There are Nike banners every 20 feet of the race, and repeated namedroppings from journalists.
Please Put Some Clothes On: the locker room scene. See Enforced Method Acting.
Raw Eggs Make You Stronger: As part of his Training Montage, Dennis attempts to drink about six raw eggs at once, but immediately spits them back up.
Reactive Continuous Scream: Dennis and Gordon, when Dennis wakes up with an hour to get to the starting line.
The Reason You Suck Speech: Whit takes that relationship-as-marathon metaphor and drags it right out of the subtext to slap it in Dennis' stunned face.
Runaway Bride: Dennis is a runaway groom.
Shout Out:
- Dennis refers to Whit as "Peter Perfect".
- The reporter refers to The Loneliness Of The Long-Distance Runner, a short story by Alan Sillitoe.
They Wasted a Perfectly Good Sandwich: The spaghetti bolognese, becomes a plot point later on.
Title Drop: by the crossdresser, and later by Whit as he pulls away in the race.
Training Montage: Parodied and played straight side-by-side.
Transvestite: who enjoys terrorizing Dennis the security guard, and is later shown running the marathon.
Ugly Guys Hot Daughter: Maya.
The Unpronounceable: Mr Gostust... Goshdash... Mr G. For the record: Goshdashtidar.
Visual Pun: Whit and Dennis edge their way past a pair of runners dressed as a tortoise and a hare.
Wimp Fight: A stellar example.
Yaoi Fangirl: the guys are in the middle of a Not What It Looks Like moment in a taxi when it stops in front of an attractive woman, who seems to like what she sees.