A Guy Thing is a 2003 American comedy film directed by Chris Koch and starring Jason Lee, Julia Stiles and Selma Blair. It was a box office and critical failure.

Paul Morse and Karen Cooper are about to get married in Seattle. During his bachelor party, Paul has a chat with one of the dancers at the party, Becky Jackson, and they find that they have an affinity for each other. Paul wakes up the next morning and is terrified to see Becky in the bed next to him.

Assuming they slept together, Paul rushes Becky out of his apartment and hopes never to see her again. He tries to cover up the connection for the remaining six days before the wedding. Unfortunately, Becky unexpectedly shows up around town and turns out to be Karen's cousin. Even worse, Becky's malicious ex-boyfriend, police detective Ray Donovan, had Becky followed and photographed. Becky and Paul meet again to steal those pictures from Ray's apartment.

Further problems arise with family and friends consistently showing up at the wrong times. Genital crabs, dirty underwear in the toilet tank, a horny best friend, and a best man/brother who is in love with the bride all provide for a week of wedding preparation hijinks. Through the snowballing of all his implausible lies and half-truths, Paul receives corroboration and support from an unexpected corner; what seems to be a coordinated network of other men, including friends, complete strangers and, to Paul's astonishment, Karen's own father; all who give the same explanation: "It's a guy thing".

Principal photography took place from November 2001 to February 2002, in Seattle, Washington and Vancouver, British Columbia, Canada.

The release date was originally slated for August 23, 2002 and then September 20, 2002 hence having a copyright date of 2002 in the credits, before finally being released January 17, 2003 in time for Valentine's Day.

The film debuted at #7 in the U.S. box office, taking USD 6,988,749 in its opening weekend, before falling to #11 the following week.^[3]

On Rotten Tomatoes, it has a 25% approval rating based on 104 reviews, with an average score of 4.1/10 and a consensus: "Wasting the talent of its leads, A Guy Thing is a predictable romantic comedy that relies on cheap laughs."^[4] On Metacritic the film has a score of 27% based on reviews from 29 critics, indicating "generally unfavorable reviews".^[5] Audiences surveyed by CinemaScore gave the film a grade "B−" on scale of A to F.^[6]

Dennis Harvey of Variety said that the film "does get slightly better as it goes along" but suggested that the multiple rewrites polished any creativity or originality out of the script.^[7][8][9]