The moral in the crude The Sweetest Thing is that women can act just as lamely and think with their libidos as much as men can. Gender reversal is the key here. All the recent lowbrow movies feature men as protagonists, getting into all sorts of situations (usually sexual and embarrassing). In The Sweetest Thing, women replace men as the stars and the objects of embarrassment. Now, instead of the men being the jerks who learn their lesson in the end, it is the women, and in particular Christina (Cameron Diaz, Slackers, Vanilla Sky). Christina hates commitment, and lives in the now. Instead of looking for "Mr. Right," she is looking for "Mr. Right Now." On the surface, she is happy, but underneath, she is looking for something more solid. She realizes this when she meets Peter (Thomas Jane, Original Sin, Under Suspicion) at a club.
Like all romantic comedies, they do not hit it off well. Peter is out celebrating his brother's wedding, and Christina is trying to cheer up her friend Jane (Selma Blair, Legally Blonde, Storytelling). Peter perfectly dissects Christina's shallow personality, which greatly disturbs and irks her. After some thought, she realizes that he is the type of person she wants. She is sick of playing games and wants something serious. She vows to find him with other friend Courtney (Christina Applegate, Prince Charming, Just Visiting). They plan to drive the of couple hours to where the wedding is, so that Christina can tell Peter her true feelings. So The Sweetest Thing is part gross-out comedy, part romantic comedy, part road trip movie, and nearly completely manufactured.
The bulk of the story by Nancy M. Pimental (who wrote for Comedy Central's South Park) is not really story, but extended gag sequences or random things like a fashion montage. The trip to the wedding and Christina's quest for Peter feel like an afterthought. As long as Diaz and Applegate can spend time dancing and goofing off, then everything else is dandy. The problem is, it's not funny when men do it in their own movies, and it's not funny here either. There's just a lot more dancing. The movie slows down significantly in between gross gags, doing the minimum necessary to sustain a story.
Another issue is that for most of the movie, Christina and Peter are not on screen together. It did not work in Serendipity and it does not work here. Director Roger Kumble (Cruel Intentions 2, Cruel Intentions) doesn't give anybody the chance to believe the chemistry between the two principal actors. As a physical actor, Diaz fares surprisingly well, but this movie is so generic that it's all for naught. Plus, it takes more than giggling and jiggling to make a difference in a movie. Jane's performance is harder to gauge, mostly because Peter has no personality. Even at less than ninety minutes, The Sweetest Thing feels long. The concept itself runs dry quickly, so Kumble has to pad it with pointless sequences to stretch it out to feature length.