Fans of Jennifer Aniston the world over think they know her. So any thudding noises you hear coming from cinemas this summer will be jaws dropping to the ground at her antics in new film Horrible Bosses.

In the comedy, in which three thirty-something men set out to murder their hideous bosses, she plays a nymphomaniac dentist called Dr Julia Harris.

Aniston can be heard spouting the sort of filth that would make a call girl blush and has trouble keeping her lab coat buttoned up while sexually harassing her dental assistant Dale, played by Charlie Day.

“I’ve never had a script come to me that allowed me to go in this direction,” says Aniston, who claims it wasn’t a meditated move to finally wave goodbye to her good girl image.

“I took the part because I loved it. And I thought it’d be a fun challenge to step out of what people usually see me do. You don’t want to play it safe all the time.”

Her choice of outfit today marks a new look too. Gone are the usual jeans and vest top and in their place is a black leather-look mini dress and studded, strappy sandals that show off her new tattoo ‘Norman’, which she had done in memory of her beloved dog who recently died.

At 42, she’s looking incredible and it’s a credit to Aniston that she’s achieved that hallowed feat: a sex symbol who appeals to women the world over.

But it’s Horrible Bosses director Seth Gordon who Aniston has to thank for casting her against type.

“It was really important to find an actress who could play Julia with all the intensity and delicious naughtiness the role deserves, and I thought it would be even better if it was someone audiences wouldn’t expect,” he says.

And it is radically different from any of her, often bland, rom com roles. Aniston puts in a fearless performance.

“It’s very vulgar and very rude, but that’s why it’s fantastic. It’s so outrageous, you get to have complete abandon and not worry if you’re being inappropriate at all. I loved that,” she says.

By way of preparation for the role, Aniston channelled some stereotypically masculine behaviour: “I thought of her as a guy, which made it that much more fun.”

Besides, she thinks it’s about time women were portrayed differently in films.

“Men are intimidated by any woman who’s sexually confident, no matter what age, and I think it’s nice to finally see that.”

Aniston admits she’s never felt more comfortable with her life, and perhaps that’s something to do with her new man, the actor Justin Theroux, who tabloids are excitedly exclaiming to be ‘The One’.

The fact they reportedly have matching gold knuckle dusters (she’s wearing hers on her engagement finger) has only added to speculation, but Aniston won’t be drawn on the subject.

Instead, she says: “I think I absolutely get more comfortable in my body – and in who I am – as I get older, way more than when I was in my 20s. I was just so awkward and uncomfortable,” she says.

Of Greek descent, Aniston was born in California but spent a year of her childhood in Greece, before relocating to New York when her actor father, John, landed a role on the daytime drama Love Of Life.

She had her first taste of acting at the age of 11 at the Rudolf Steiner School’s drama club, before moving on to New York’s High School of the Performing Arts. After graduation, she won roles in off-Broadway productions.

“I started out in New York, in things that aren’t remembered,” she laughs. “I love the theatre and I’d love to go back to it, if the right thing presented itself.”

In 1989, she landed her first television role as a series regular on Molloy, followed by roles in Ferris Bueller, Quantum Leap and Burke’s Law.

Then in 1994 she starred as ditzy Rachel Green in Friends. By the time the final episode aired 10 years later, she’d amassed six Emmy Award nominations, seven Screen Actors Guild Award nominations and two Golden Globe nominations.

“I still get people referring to me as Rachel,” she says, fondly.

Though she’s branched out into darker projects such as The Good Girl opposite Jake Gyllenhaal and the thriller Derailed alongside Clive Owen, it’s the roster of rom coms, from Along Came Polly and Marley & Me to The Switch and Just Go With It, for which she’s become synonymous.

Speaking in a voice that sounds a little weary, she admits critics haven’t always been kind about her abilities or film choices, and says she wouldn’t mind if she felt the comments were justified.

“It feels really personal, as opposed to constructive critiques of the performances. It hurts and it’s really inconsistent,” she says.

As the subject of worldwide tittle-tattle for the past two decades, perhaps it’s no surprise to hear she’s ready to embrace time away from the intense media spotlight.

“Yes, I’m going to take a break,” she says.

“Travel, live a little, I don’t know what I’m going to do. And that...” she adds with a grin, “is the fun part.”

Perhaps she might have time to plan a wedding...