For all that The Script's singer has comfortably settled into a role as a Saturday-night TV favourite after his stint as a judge on The Voice UK, he can certainly let fly with several expletives when the mood takes him.
"You hear about the Gallagher brothers kicking the s*** out of each other after gigs – that's me and Mark with songs," he says, describing the relationship between himself and The Script's guitarist and co-songwriter Mark Sheehan. "We're trying to kick the s*** out of each other by writing better songs than each other. I'm like, 'See this, try to beat that.' And he's like, 'F*** you, watch this.' It's real McCartney and Lennon stuff. It's f***-you one-upmanship with the band."
It's a tactic that's done The Script no harm at all, given the strong sales of their first two records. Their third album, #3, is released on Monday and will no doubt garner the same results, if not better, while their gig at the O2 ABC in Glasgow tomorrow night sold out in a matter of minutes.
That said, #3 is their first record since 31-year-old O'Donoghue became more than just a singer with a popular band. He's now a familiar TV face who has appeared alongside Sir Tom Jones, Jessie J and will.i.am (who guests on The Script's latest single, Hall Of Fame). Audience ratings may have dropped during the show's run, but it was certainly huge mainstream exposure for the Dublin native, though he is swift to reject the notion that he is now set to become a Cheryl Cole-style figure.
"I don't want to be a TV celebrity because most of them are only known for being a TV celebrity," he says, firmly. "Everyone knows I'm in a band, and that's the main thing about me."
That may be true, but there's no doubt eyeballs and ears were attracted to The Script as a result of the show, even if the band were in rude health beforehand. It has, he admits, also meant a number of people now regard themselves as being on first-name terms with him.
"I was warned before I went on [The Voice UK] that when you're on television, people think they know you," he says. "They've allowed you into their life, and I'm grateful for that. I'm also grateful no-one has hated me! The BBC did a great job of editing me so I didn't come across as the idiot we all know I am - No-one coming up to me on the street has been saying anything bad about me or my artists. It is strange, though, because everyone in the UK now knows me and I don't know them."
Chatting with strangers aside, for the affable, quick-speaking O'Donoghue the main benefit of appearing on the programme was that it offered a chance to get a more credible musician on such a show, rather than another plain pop star. He also believes his judging and coaching stint (he mentored the show's runner-up, Bo Bruce) won't affect people's opinion of his band's music.
"I just asked the lads in the band if I should do it or not, and what they thought the pros and cons were of it. They said it's a show you can hold your head up high about doing as at least there's some musical integrity there. That was a big plus and I thought it was really important that bands in general were being represented on it, whether it was One Republic, Stereophonics, at least you can play a guitar up there."
There may be a few eyebrows raised at that choice of comment, given that The Script are hardly buccaneering revolutionaries setting the blue touch paper alight and burning manufactured pop to the ground. Their songs are often sculpted for radio airplay, all soaring chord changes and emotional vocals, a trend which carries through neatly on to #3, where most of the 10 tracks could easily be singles.
Given that both O'Donoghue and Sheehan worked as producers and songwriters in the US for a spell, it's unquestionable they know how to pen a pop tune. The singer doesn't deny that such knowledge clearly helped the band (who are completed by drummer Glen Power), and his advice for other groups runs towards more prosaic suggestions, too.
"That production background has helped on a fundamental level, and that's what's missing for many artists in the industry," he argues. "We came from the industry first, so when we came into this with ideas as an artist, we also understood that there is another game to be played. You can't be a band making demands and wanting to do your thing as you have to look after everything else, and the most important thing for bands is money.
"Where are you going to get the money from to keep the band afloat? It's one thing getting signed or a publishing deal, but what are you going to do with the money? Most people get the money and just spend it, like they think: 'That's it, it'll be coming in for ever' – and that's stupid. When we got our money, we put it in a bank and started paying ourselves a wage, and that was the smartest thing we're ever going to do."
Any suggestion that what The Script try to achieve on their albums is purely driven by needing to have a hit is sternly dismissed, however. O'Donoghue is adamant that the band's songs are led by their emotions, and points to examples on #3 such as If You Could See Me Now, which deals with the loss of the singer's father and Sheehan's parents at a young age. The Dubliner believes there needs to be something for the group to say before they can contemplate recording, although the actual sessions tend to be where he feels most in his element.
"We always get in an emotional state because there has to be a reason to be writing an album and there needs to be something strong enough that you want to say that the rest of the UK will want to hear. So you can talk about what you want in it, but you can also keep to those parameters and those lines [for getting on the radio], and everything else comes really easily. It might sound strange, but we're most at home during the recording process. That's probably because we all come from producing backgrounds, not the stage – I feel most at home, in the world, in a recording studio."
Perhaps that explains why he's so at ease writing about his emotions for The Script's albums. The band's songs often feature emphasis on romantic break-up and personal issues, and it's clear his songwriting can also double as emotional therapy.
"I think that the more you talk about a problem, the more it helps, and that's the amazing thing about songs – by singing it every night, it becomes easier to deal with. I've always been honest and have my heart on my sleeve, and when we release an album the rest of the UK is wearing the jacket."
Perhaps that's The Script's success in a nutshell, then: big emotions mixed with catchy tunes equals global domination. Make no mistake, that does seem to be one of the band's aims, with O'Donoghue listing a career highlight as playing the MTV Asia Music Awards because of the amount of people that were watching them on TV. And he's not going to stop there -
"We write songs that we want to get on the radio because that's the portal to getting our ideas to the rest of the world," he concludes. "Other bands who don't conform to that, who write eight-minute concertos with no lyrics and lots of solos, definitely aren't getting played on the radio. If you have that knowledge of what radio wants, you can do whatever you want within that knowledge.
"I never wanted to be in a band that are playing to 30 people but they are all amazing musicians doing 10-minute long songs. F*** that. I want everyone in the world to at least hear a Script song once. You have to have big dreams or else you'll fall flat on your f****** face."
The Script play the O2 ABC, Glasgow tomorrow and release #3 on Monday.