In theaters

TWILIGHT, directed by Catherine Hardwicke, written by Melissa Rosenberg, 122 minutes, rated PG-13.

The slight new Catherine Hardwicke movie, “Twilight,” is about the heated and potentially undeadly physical attraction that ignites between two hot-and-bothered teens.

One is a vampire who has been 17 since the turn of the last century. The other is a young woman who apparently is so hot for this guy, she’s willing to offer up her throat to him regardless of the repercussions that will follow.

Her name is Bella Swan and she’s played by Kristen Stewart in a performance that best can be described as slack-jawed.

I’m not suggesting that Bella is stupid – her inward turmoil is meant to reflect depth – but given the way Stewart keeps her lips parted throughout the movie, Bella seems forever dumbstruck, as if she’s caught in a state of eternal awe.

It’s tough to blame her. When she moves to Forks, Wash., to live with her single father, Charlie (Billy Burke), who is the town’s police chief, the poor girl’s hormones are at full boil. This proves problematic when she shows up for chemistry class (naturally) and meets the mysterious Edward Cullen (Robert Pattinson), whose dark eyes, enormous hair and bleached face apparently are so dreamy, Bella is pulled toward him by urges previously unknown to her.

At first, Edward is having none of her – he’s rude, sullen and swarthy. And then he’s kind of into her, literally saving her life when a van nearly smashes into her. What’s Bella to make of this? Since her lips are parted, it’s clear that she doesn’t know, though soon she’s fantasizing about Edward as much as she’s questioning him. After all, when Edward saved her life, he literally stopped that van with an outstretched hand.

The film, which Melissa Rosenberg faithfully based on Stephenie Meyer’s best-selling novel, is so purple, you’d swear it was a bruise.

This is especially true when Bella and Edward give in to their hormonal rampages, throw garlic cloves to the wind and fall deeply in love with each other. At that point, Bella knows that Edward is a vampire who has killed people, but since he’s a reformed vampire (he and his family responsibly suck only the blood of animals), that’s enough for her – she’s into him. She wants him. She’s ready to go for it. But as for Edward, who lusts for her blood but who can’t bring himself to kill her for it, their relationship must remain chaste, which causes Bella to pause and her lips to part.

It doesn’t exactly take the brightest bulb in the room to figure out what’s going on here. If and when these two do go all the way (a sexual relationship might leave Edward in such a frenzy that he’d sink his fangs into her), they must wait until they’re mature enough to make that decision, should it ever come.

And there you have it. While a subplot involving a band of evil vampires does give the movie its welcomed moments of action and Edward’s family does come through with a few necessary laughs, “Twilight” really is a glum film about the perils of teen intimacy. Here, life literally hinges on abstinence and morality. While those are fine qualities for any movie aimed at tweens to promote, “Twilight” is unfortunately so sloppy and shallow, your own lips part. This is a movie unable to make you feel anything profound for its characters.

Grade: C-

On DVD and Blu-ray disc

TROPIC THUNDER, directed by Ben Stiller, written by Stiller, Justin Theroux and Etan Cohen, 106 minutes, rated R.

Ben Stiller’s “Tropic Thunder” has a hilarious opening that establishes its main characters in ways that are so rich, it won’t be explored here. But it is ingenious. What can be said is that it cleverly introduces audiences to a group of famous men struggling to find themselves midcareer by starring in what they hope will be a hit.

Those men include Tugg Speedman (Stiller), a muscled action-adventure type on the downside of fame; Alpa Chino (Brandon T. Jackson), a rap star best known for his popular soft drink, Booty Sweat; Jeff Portnoy (Jack Black), a heroin addict beloved the world over for starring in such comedies as “The Fatties: Fart II”; and Kirk Lazarus (Robert Downey Jr.), an Academy Award-winning thespian who takes his craft so seriously, he undergoes a controversial pigment transformation to become a black man for his latest role in the Vietnam War movie all are appearing in now.

About that movie. Shot in some faraway jungle overseas and based on the life of Sgt. Four Leaf Tayback (Nick Nolte), who lost his hands in combat, it eventually leads all down one disastrous path, especially when egos get in the way, as egos tend to do, and when things go unexpectedly wrong for their director, Damien Cockburn (Steve Coogan).

Making matters worse is studio head Les Grossman (Tom Cruise), a hirsute mess determined not to lose a dime just because these prima donnas are having a tough time making their movie. Bullying them at every turn, Les instills in them the sort of foul-mouthed fear that drives the action forward.

What springs from this is an unwieldy plot that relies so heavily on surprise to sell its laughs that revealing more would ruin the adolescent pleasures laced throughout the script. This isn’t a consistently funny movie, but when the laughs do hit, it’s as if you’ve been rocketed to the moon.

Grade: B