Sherman 'Tank' Turner (Dane Cook) is a help line operator and a ladies man with a hobby: If a guy loses a girl and wants her back, he gets in touch with Tank and pays him to take the girl on a bad date. Throughout the evening Tank inevitably behaves in the most moronic fashion causing the girl to realize that her ex was not really such a bad guy after all and get back to their ex.
He shares an apartment with his step cousin Dustin (Jason Biggs) who has fallen for his work colleague Alexis (Kate Hudson). Dustin takes Alexis on a date and confesses his love but she insists they remain friends. After the date Dustin explains his situation to Tank who volunteers his services as a good friend (instead of having to pay for his services as usual). Dustin initially turns him down, not wanting Tank to be close to Alexis, but the next day sees Alexis flirting with another co-worker and begs Tank to take Alexis out. He accepts.
Tank bumps into Alexis and they arrange to go out. He behaves badly all night but Alexis is too drunk to care. When he drops her off she expects him to come in but he resists the temptation out of loyalty to Dustin. Alexis calls Dustin but when they meet she explains that her date with Tank has motivated her to see other men. Dustin sends Alexis roses and an apology poem in Tank's name. Alexis calls Tank at work and berates him for leaving early the previous night. Tank goes to see Alexis and they end up having casual sex on a regular basis while Dustin begins a series of desperate attempts to stay friends with her after all.
Dustin prepares to go on a date with a single mother but when he arrives to pick her up, she is breast-feeding her child. Dustin, in an effort to be funny, awkwardly remarks that he would like to have what the baby is having. The woman, now creeped out and furious, yells at Dustin and throws him out, cancelling their date. Distraught, Dustin goes to Alexis's home to see her but is told by her roommate that Alexis was busy upstairs with the guys she has been having sex with regularly. Dustin, even more upset and refusing to leave, starts to walk up the stairs only to discover that the man Alexis has been sleeping with is actually Tank. Tank and Dustin get into a fight and go separate ways. Tank's feelings for Alexis have now grown and he decides to consult with his father (Alec Baldwin). After meeting with his father, he has doubts that he is deserving of a serious relationship with her. While attending the wedding of Alexis' sister Rachel (Diora Baird), he realizes that she is one of his previous bad dates. The groom, Josh (Taran Killam), asks Tank to keep quiet about his use of his services. After overhearing Alexis telling Rachel that she has fallen for him, Tank's guilt causes him to sabotage their relationship and call Dustin to apologize to him.
Dustin arrives at the wedding reception and reveals Tank's schemes to Alexis. Tank points out his clients, including the groom, and is punched and thrown out. Alexis, distraught from the fact that Tank used her, and that Dustin played to cheaply win her, never wants to see either of them again. Later, while talking with Dustin and his father, Tank realizes that he loves Alexis and they encourage him to reconcile with her. He finds her and jogs with her for a few miles, in the attempt to make amends, but Alexis is unmoved.
Three months later, Tank is on a date when Alexis sees him and spontaneously decides to sabotage the date by embarrassing him. She walks up to him and throws wine in his face, ruining his date. Then continues to try embarrass him by stating to the whole room that he left her pregnant. He soon catches on to her "joke" and they then continue to throw insults at each other (some of which shadow previous insults they threw at each other at their second meeting), each trying to best each other in a "play argument" of insults and bantering. After which they reconcile with a kiss. The film ends suggesting their relationship is back on. As the film's titles roll up, it is shown/suggested that Dustin and Alexis' roommate Ami (Lizzy Caplan) hook up (or at very least have a sexual encounter if not actually a relationship). It's left up to the audience to decide.Dane Cook as Sherman 'Tank' Turner, a help line operator with a hobby of taking girls on horrible dates.
Kate Hudson as Alexis, Dustin's co-worker and Tank's love interest.
Jason Biggs as Dustin, Tank's best friend and roommate.
Diora Baird as Rachel, Alexis's sister and one of Tank's bad dates.
Alec Baldwin as Professor William Turner, Tank's father.
Lizzy Caplan as Ami, Alexis's best friend and roommate.
Taran Killam as Josh, Rachel's groom.
Malcolm Barrett as Dwalu, Tank's friend and colleague from the call center.
Riki Lindhome as Hilary, a deeply Christian girl.
Mini Anden as Lizzy, one of Tank's one-night-stands.
Robert Fennessy II as the Bartender
Brad Garrett uncredited cameo as angry customer on phone.
Nate Torrence as Craig
Joshua Rego uncredited cameo 3 scenes
"Do Me" - Jean Knight
"You're No Good" - Linda Ronstadt
"My Best Friend's Girl" - The Cars
"Love is Like Oxygen" - Sweet
"99 Red Balloons" - Nena
"Crimson and Clover" - Tommy James and the Shondells
"At Last" - Etta James
"Have a Little Faith in Me" - John Hiatt
"Save Some" - Glacier Hiking
"Blue" - Malbec
"Always Where I Need To Be" - The Kooks
"Pop That Pussy" - 2 Live Crew
"Separate Ways" - Teddy Thompson
"Best Friends Again/I Love You" - John Debney
"The Man Comes Around" - Johnny Cash
The soundtrack available for purchase does not include every song.
The film was poorly received by critics. Review aggregation website Rotten Tomatoes gives the film a score of 14% based on 58 reviews, with a consensus that "My Best Friend's Girl spends too much time being vulgar and offensive, leaving little room for laughs." Metacritic gives film had an average score of 34% based on 13 reviews, indicating a generally negative response.
My Best Friend's Girl earned a Razzie Award nomination for Worst Actress (Kate Hudson; also for Fool's Gold). Dane Cook also harshly criticized the poster for the film on his Myspace blog.
The film opened at No. 3 at the North American box office making $8,265,357 USD in its opening weekend. It went on to gross $41.6 million worldwide.