While living in London a few years ago, Kiwi Antonia Baker broke an unwritten code of etiquette and began dating her friend - and flatmate - James Vincent. She'd moved into the flat in 2006 and the pair "hooked up" the following April. "Yeah, I screwed the crew. You're not supposed to do that," says Baker.
Her initial friendship with Vincent was strictly platonic. "We were really good friends. He's a bit of a comedian," says 25-year-old Baker. "He didn't let me miss my family at all, just made my shift to Britain so easy."
In the beginning Baker and Vincent enjoyed meals at the local pub, trips to France to watch rugby and travelled through Europe together without there being a hint of romance or attraction. The relationship could well have continued like that had it not been for an accident that proved to be a turning point.
"I was hit by a car, cycling to work; and when he saw me hurt he began to think how terrible it would have been to lose me, and he realised he had feelings for me. After that we started hooking up."
Their other flatmates soon guessed what was going on. "I think we started sitting together on the couch and sneaking into each other's bedrooms," says Baker, who'd had no designs on Vincent, 24, until he professed his own feelings. "He's a wicked guy and I was a really, really good friend of his but I'd never looked at him like that. I was always saying to my girlfriends, 'James is such a good catch' but I just wasn't attracted to him. But sometimes if people start looking at you differently you start seeing them with different eyes too."
The couple are now settled in Hamilton and due to get married next January. Baker says she has "always preferred to hang out with guys. I just find guys easier than girls. I work in horticulture and I'm not really a girly girl who talks about fashion or makeup. And men are more straightforward, they don't hold grudges. They crack me up."
She believes that having had such a strong platonic friendship has only strengthened her and Vincent's relationship. "By the time we got together we knew each other inside out. We were such close mates. I'd talked about my previous relationships and he'd had some girlfriends while I was around. It might not be for everyone but I thought getting to know each other beforehand was a really good thing. No skeletons to come out of the closet. For me it meant I didn't have to waste time trying to get to know someone who wasn't going to be compatible."
The concept of platonic relationships with people of the opposite sex is endlessly fascinating and a subject of great debate. For every 100 per cent non-sexual friendship that exists there's guaranteed to be a supposedly platonic friendship where one of the parties has ulterior motives or an unprofessed adoration for the other.
Then there are myriad examples - not just in real life but in popular culture, such as Friends, When Harry Met Sally, My Best Friend's Wedding and Reality Bites - of friends who become romantically or sexually involved. A survey of more than 1450 members of dating site match.com found that 62 per cent of people had in fact "crossed-the-line" with friends.
A Psychology Today article entitled "Can men and women be friends?" found that while platonic relationships were "tricky", the consensus among those interviewed was that they're not only possible but desirable.
"I suspect that the male-female taboo boundaries are being broken down a bit, so it's not so scary to have a friendship with a man or for a man to have a friendship with a woman," says Auckland psychologist Sara Chatwin.
Chatwin, who herself has predominantly male friends, believes that platonic relationships don't have to be complicated. "I like the way men go about things. For me a really pragmatic masculine approach is something I like. I like to listen to their advice. I like their perspective," she says. "I think of [my best mate] as somebody I could talk to, go for a run with, ring up if I had a problem with the computer ... but I don't abuse my privilege as his friend ... I don't interrupt his personal time. We just have a very pure friendship and, of course, there's nothing romantic, nothing sexual and nothing untoward."
And the fact that Chatwin is married while her closest friend has a girlfriend is no impediment to their friendship. "You have to show your opposite-gender best friends and their life and their partner a lot of respect. Like, I wouldn't bug him during his time with her." She believes that respective partners should be introduced to each other in order to diffuse any potential misunderstandings. "I don't think there necessarily needs to be jealousy. I think if you're open and above-board with things there probably shouldn't be jealousy. I've seen it come unstuck when [romantic] partners feel like they're not the special one in the relationship because their person has somebody else."
Professionally, she has encountered examples of platonic relationships that shift into more intimate territory. "The boundaries get blurred and you look at people in a different light and I have seen relationships form in this kind of a way. If at some point it dawns on someone, or both of them, that their friendship is more than a friendship, then it's not a friendship any longer. It's moved into a very awkward kind of a space that needs to be dealt with."
Chatwin advises platonic friends to set ground rules from the outset, to be alert for signs their relationship is changing. "It pays to make sure that there are parameters, there are boundaries."
Wikihow.com goes so far as to list eight steps on "how to be just friends with a member of the opposite sex". Their advice is to "involve the significant other(s)", "minimise sexual tension", "prevent borderline situations" and "be careful with your decisions".
Aucklander Debbie Brown, 31, estimates that about half of her friends are men. "My guy mates are very keen to meet my female friends," she says, but the credentials for friendship are the same regardless of gender. "It's simple. You just have to be a decent person and get on with each other. Men are just people, too. I think women forget that sometimes. They're not that difficult to understand. Sometimes we mystify them in our own minds."
Male friends come in handy when Brown's car needs repairing. "It can save me $200 a time. Mind you, it works both ways. Sometimes I think [close friend] Nick just comes around for a feed, to scab my cooking. And my guy friends definitely play pool better."
But trouble can arise. Romantic partners don't always accept their other half's platonic friendships. "My last boyfriend couldn't handle my guy mates at all," says Brown. "He had a real issue with it. He was jealous and he couldn't understand I could like someone and be friends with them without jumping into bed with that person. He acted like a toddler and sulked whenever I saw my guy mates."
Like Baker, Brown has experienced a friendship that became a romance. "I found him attractive and I knew our personalities were compatible. The relationship was a lot better, with trust established and a lot of that early groundwork already done," she says. But it didn't last and Brown discovered her ex-partner had fancied her from the outset of their "platonic friendship".
Lawyer Mark Russell attributes his large number of women friends to attending co-ed Macleans College, then taking a female-dominated university course. "You spend extended periods of time with the same people. I was at school for five years and law school for five years, so you're seeing them on a day-to-day basis. Then all of a sudden you don't see them as necessarily a girl or a guy but as one of your mates, part of that group."
Russell, 26, typically socialises with his female friends in a group or on one-on-one lunch dates and relishes the opportunity to discuss topics that men tend to avoid. "I think you can talk to girls about different things." Such as personal and relationship matters? "Yeah. They enjoy listening to it. You know, when girls talk to girls they talk about guys that they're seeing and they'll go into every single detail. But if a guy's just met a new girl his guy friend's going to say, 'how is she?', the other guy will be like, 'she's fantastic'. And that'll be it. You won't go into all the details."
New York psychologist Linda Sapadin made a similar observation in Psychology Today, saying that men benefit more than women from a platonic friendship: "What [the men] reported liking most was talking and relating to women - something they can't do with their buddies."
According to Russell, the nature of platonic friendships often alters as the parties involved acquire a romantic partner. "Sometimes it changes significantly. You might see a girl a lot just as friends and then when she does get into a [romantic] relationship, you might not see much of her for a while. I guess when I was in a relationship there wasn't much jealousy or anything like that. If I was going out at night I'd go with my girlfriend but if I was going for a lunch with someone it would be [with] whoever's around."
No exploration of cross-gender friendships would be complete without a look at women with gay male friends. It's a subset of platonic friendship beloved of Hollywood - think Will & Grace and Sex and the City. "Stereotypically and through the media and sensationalised are those ideas of the fag-hag and the gay man that hangs with the women," says psychologist Chatwin. "A lot of women would say they're a bit less threatening. That's the clichéd response."
Sarah O'Brien, 31, reckons 90 per cent of her friends are gay men. "I have my gaggle of gays. They hang in a pack. There's never just one," she says. "They all dance. They're always on the dance floor." O'Brien, a flight attendant, and her friends enjoy a social time involving coffee dates, gym appointments and the odd spot of karaoke.
"They've got disposable incomes and no family commitments [so are] able to just do things like that."
So O'Brien holidays with eight gay men? "Yeah, that's exactly how it works. I'm always pretty much the only girl. It's actually quite good I suppose, because you do get the attention," she says. "I sleep in the same bed as them sometimes. It's not an issue. I don't choose them because they're gay. It just happens to be like that. It's just who I enjoy hanging out with."
And of course, in common with her gay friends, O'Brien, currently single, has a keen eye for the perfect man. "I can appreciate the same things they can."