Anyone who ever found a boiled bunny on the stove knows breaking up with a woman who won’t be ignored can be extremely dangerous. What if your ex is a super hero with self-esteem issues who doesn’t like bad news? Meet Matt Saunders (Luke Wilson), an amicable, good-looking guy who comes to the rescue of mousy gallery curator, Jenny Johnson (Uma Thurman). Looks can be deceiving. Underneath the Plain Jane facade hides G-Girl, who can save humanity but can’t find a man.

So when Matt reverses the tables and saves her, Jenny/G-Girl is instantly smitten. Suffering from a history of bad relationships, Matt is hesitant to get involved with Jenny, who momentarily excuses herself from their first date to put out a burning building.

At first, Matt is turned on by Jenny’s Jekyll and Hyde act, as she goes from kitten to mountain lion in one pounce. What man wouldn’t want headboard-banging sex? When Jenny finally introduces Matt to her alter ego, he’s frightened by the revelation. His fear escalates when he learns Jenny/G-Girl has an extremely jealous streak and is capable of making his life a living hell.

Great premise, good cast, OK direction, but this hybrid of Fatal Attraction and every super-hero movie since Spider-Man doesn’t always go the distance. My Super Ex-Girlfriend starts off promising enough with a good set-up and likable characters, but once it drifts over into a comic revenge thriller, it loses focus and becomes a parade of digital jokes. Some work, others don’t, but we expect more from veteran Simpsons writer Don Payne. The characters are conventional, forcing the cast to rise above the material.

They frequently do, as during Matt and Jenny’s first date tango, when the characters are still exploring their boundaries. The scene is funny because we are in on the joke. Once Matt is in on the joke, the film has nowhere to go but to become an exercise in over-the-top chaos. G-Girl’s obsession is played for laughs, even when she ventures over into Fatal Attraction territory. So when she tosses a live shark into Matt’s bed or hangs him from the Statue of Liberty’s crown, we never take the threat seriously.

Director Ivan Reitman (Ghostbusters) engages us in these shenanigans, but he never makes us care. It’s functional but not fantastic. Thurman goes from mouse to kitten with a whip without missing a stroke, and she’s extremely appealing as a neurotic woman on the edge. Wilson is likable as an average Joe who can’t see beyond Jenny’s Clark Kent disguise. He’s really in love with a co-worker (Anna Faris, less zany than usual) who is dating someone else. This dynamic should provide more laughs than it does. While the irony isn’t lost on Matt’s best friend, Vaughn (Rainn Wilson, The Office), the payoff isn’t as promising as the set-up.