Is Isla Fisher crazy like a fox? ‘Definitely, Maybe’

She’s best known for playing the ditzy, sex-mad sprite who seduces Vince Vaughn in “Wedding Crashers” but Isla Fisher wants you to know she’s no kook.

In “Definitely, Maybe,” her latest romantic comedy, Fisher flaunts her versatility as a Bill Clinton campaign worker who’s wary of romance. In the words of writer/director Adam Brooks, Fisher’s April is “passionate, caustic and brilliant.”

“What really piqued my interest about “Definitely, Maybe’ is that I wasn’t playing the crazy, larger-than-life person,” says Fisher, who grew up in Australia, the daughter of Scottish parents. “I was playing the heart of the movie.

“My character is outspoken and feisty. She’s someone who’s afraid of love and then learns not to be afraid. I thought that was pretty sweet.”

In the movie, opening today, Ryan Reynolds stars as an about-to-be-divorced advertising exec who sits down with his daughter (Abigail Breslin) to spin the story of his life and loves.

He changes the names of his three ex-girlfriends (Fisher, Elizabeth Banks and Rachel Weisz) so his daughter will have to guess which one turns out to be her mother.

When Fisher read Brooks’ inventive screenplay, which is set in New York during the ’90s, she flipped for its mix of social commentary, comedy and romance.

“I’m not a fan of the slick, Hollywood romantic comedies where you know in the first act who’s going to end up with whom,” says the actress, 32. “Those movies aren’t really realistic. In this movie, all the women are normal people with flaws. There’s no good or bad characters; this is a realistic love story.”

Offscreen, Fisher is engaged to Sacha Baron Cohen, with whom she has a 4-month baby daughter named Olive. Ask her if being a mom has changed her life and she laughs but declines to answer.

“Motherhood is definitely my favorite topic in my personal life and I won’t shut up about it,” she says. “But it’s not something that I want to discuss publicly just because of the amount of attention it draws to a small person who really didn’t choose the exposure.”

Fisher is just as cagey when it comes to talking about Cohen. All she’s revealed about the “Borat” star is that he’s a humongous Monty Python fan.

“We can just go back and re-watch the [Python movies] everyday,” she says. “I’m not a big follower of emotionally draining, really dramatic movies where you leave exhausted, without a will to live.”

Already signed up for another romantic comedy called “Confessions of a Shopaholic,” Fisher says her dream roles include playing Imelda Marcos, Katharine Hepburn (“Cate Blanchett did such an amazing job with that one already, though”), Joan of Arc and Babe the Pig in the “Babe” movies.

“I do such a great pig noise,” Fisher says, offering up a demonstration. “I would’ve loved to have done those “Babe’ squeals.”