Actor Allusion: Near the end, as Kym is watching her mother leave the wedding early, she is interrupted when her father comes up to her with one of the wedding guests. He tells his daughter that the woman "just lost an office assistant" and she'd be perfect for the job.
Bitter Wedding Speech: Kym, who has just gotten out of rehab, makes a speech at her sister's rehearsal dinner apologizing for her past actions because she is jealous of the attention her sister is getting.
Damage-Proof Vehicle: Kym, angry after a fistfight with her mother, purposely drives her father's Mercedes off the road, over a road sign, into the woods and then crashes into a rock. Although the airbag deploys, when we see the car in the morning light, the front end isn't even dented.
Dinner and a Show: Subverted for the most part. Much of the escalation happens when the family is at home, but it's hard to have any privacy when the wedding party is in the same home at all times.
Dysfunctional Family: Rachel and Kym's family. Lampshaded by Kym during her speech at the rehearsal dinner.
Foreshadowing: Pay attention to what Walter says in the very beginning of the movie "Did ya kill anybody recently? Run anybody over with your fucking car? At first, it seems like the ramblings of a clearly unstable person, then you find out that Kym accidentally killed her younger brother by driving into a ravine while high.
Bucky is the unstable pyromaniac acquaintance of Kym in rehab.
It's All About Me: Kym is so self obsessed she throws a tantrum when she realizes her sister's wedding is not about her rehabilitation.
Not to say that Rachel doesn't have her moments, accusing their dad of "defending" Kym.
Kym and Rachel seem to actually be a variation of The Glorious War of Sisterly Rivalry in which Kym is out to prove that she's better and Rachel is, well, getting married. Rachel even pulls the news of her pregnancy out during a heated argument. Everyone cheers up and congratulates her, while Kym is left angry, miserable, and still unable to settle things with her family.
Jitter Cam: Demme wanted the film to look like "the most beautiful home movie ever made", so he eschewed the usual practice of setting up shots before filming scenes, leaving the cinematographer and his crew free to react to the scene the way they thought best as it played out.
Leave the Camera Running: At times, it looks like the movie was cut together from footage the guests took with their camcorders.
Mood Whiplash: Realistically for a wedding weekend where one member of the family is fresh from her latest stint in rehab, scenes can go from tense dysfunctional-family drama to lighthearted and joyful, then back again, within minutes (The dishwasher scene is a prime example).
Off The Wagon: Averted. Despite the fact that she's in a situation that would be fraught with triggers even under the best of circumstances, and the many times we see her going off by herself, Kym stays clean and sober through the weekend.
Reality Subtext: The dishwasher scene is based on a real event that occurred at screenwriter Jenny Lumet's house involving her father, the veteran director Sidney Lumet, and Bob Fosse.
Left the Background Music On: Non-humorous example; the background music is generally the sound of the wedding band practicing prior to the big day, and the father asks the musicians to stop playing during a very intense emotional moment
Throw It In: Between takes, Anne Hathaway asked the director Johnathan Demme if the wedding band was going to be playing throughout the scene. He told her if she didn't like it, she should "do something about it." So she did.