Of all the gross things in “Good Luck Chuck,” the worst is a throwaway: In the midst of this raunchy sex comedy, the film’s dentist hero casually admits that he annually travels to Guatemala to help poor people with their teeth.

Well, now I feel much better about him. If he were merely a clueless womanizing jerk, it would be difficult to sympathize, but the Guatemalan poor people thing makes it much better.

“Good Luck Chuck” is a dirty little movie featuring Dane Cook, a comedian (seen lately in “Employee of the Month”) who seems to have captured the imagination of much of the country in recent years. Cook plays the dentist, who was hexed in childhood with a unique problem: Every woman he sleeps with will find lasting happiness with the next man she dates.

A premise can be stupid and still carry a movie. But “Good Luck Chuck” is bad because not only is the premise stupid, everything else is off: the timing, the direction, the acting.

It goes sour from the prologue, an unusually distasteful make-out scene involving kids at a party, to the end credits. Stick around long enough and you’ll get to see Cook simulate a sex act with a plush toy.

In between, there are some incredibly stock jokes. Heavily accented Asian man singing karaoke? Check. Sex with a morbidly obese woman? Check. Sidekick who’s even raunchier than the hero? Double check.

Actually, the best friend is one of the film’s few bright spots, if only because the role is played by Dan Fogler, who scored nicely in last month’s “Balls of Fury.” Fogler, a Tony-winning actor who has antic traces of John Belushi and Sam Kinison in him, is a true riot, although his character (a doctor who went into plastic surgery to be around the breasts) is despicable.

Jessica Alba brings her snooze-inducing prettiness to the leading lady, a penguin expert. She shows great discretion with only one partially nude scene; the other women in the film are generally undressed.

It’s an R-rated film and there’s a lot of sex in the movie. None of which seems to faze Dane Cook, who wears the same indifferent expression throughout. He’s a curious non-presence, which might be the best reaction to being in this movie, come to think of it.

Jessica Alba and Dane Cook star in “Good Luck Chuck.”