40 Days and 40 Nights (R, 2002)

After being dumped by his girlfriend, Matt (Josh Hartnett) gives up sex for Lent. Enter the lithe and lissome Erica (Shannyn Sossamon of A Knight's Tale), whom he enjoys getting to know without jumping into bed. After a while it becomes awkward, and when she finds out what he's doing and that there's actually a website devoted to whether he'll last for 40 days, she feels hurt and betrayed. Then Nicole (Vinessa Shaw), the girl who dumped him, re-enters the picture.

At the heart of a sex farce is someone who wants to have sex (preferably illicit) but is amusingly thwarted. This gives us the best of both worlds, as we get to vicariously enjoy the illicit possibilities and feel righteously smug about the agonies the characters go through in pursuit of their quest. The problem these days is in finding believable excuses for keeping the characters apart. Not quite in the category of believable, even within the low-credibility threshold of a comedy, is this movie's premise.