Cherubic and slightly disheveled, bedecked in his I'm-a-rock-star-but-I-dress-like-a-bike-messenger finest, Fall Out Boy singer/guitarist Patrick Stump radiates a low-wattage, shy affability-in other words, you’d never know he was a rock star. “I find the whole thing hysterical,” he admits. “Rock stars are supposed to be thin and good looking. They’re supposed to wear eyeliner and get into trouble. They’re supposed to put naked pictures of themselves on the Internet.” He smiles and snaps his fingers. “Hey! I know one of those guys.”

Stump’s reference to his songwriting partner, Fall Out Boy bassist Pete Wentz, couldn’t be more unsubtle. And subtlety wouldn’t go very far in the land of Fall Out Boy, one of snarky, au courant lyrical put-downs and concision-challenged song titles (try "I Slept With Someone in Fall Out Boy and All I Got Was This Stupid Song Written About Me” on for size). Since the Chicago-based band (which also includes guitarist Joe Trohman and drummer Andrew Hurley) busted out a mega-hit with their major label debut, 2005’s From Under the Cork Tree, Stump, who favors Gibson Les Pauls  and SGs, says it’s been a challenge to write material that “can stimulate the group musically but still hit the audience dead-center. We throw out half the stuff we write. We’re fine for going for the throat, for being, you know, obvious, but it has to be our own kind of obvious.”

At close to two million copies sold since its release early this year, Fall Out Boy’s latest album, Infinity on High, has pleased the faithful. A tight, cogent affair, produced by longtime "fifth Fall Out Boy" Neal Avron (who helmed Cork Tree), with R&B hitmeister Babyface helming two cuts, it's a portrait of a band bravely refusing to surrender to success-induced stasis and rocking with winsome authority.

The group’s playful, erratic sense of rhythm, their herky-jerky hardcore-esque guitars, envelope rather than crush you. And as always, Wentz’s titles refuse to conform, as evidenced by tracks such as “I’m Like a Lawyer With the Way I’m Always Trying to Get You Off.” But the real revelation is Stump himself. On the funkified “This Ain't a Scene, It's an Arms Race" and the Keef-riff driven "The Take Over, The Breaks Over," he’s shed the last vestige of emo in his voice-the affected “yelping” style of singing that has become predictable and genre-specific- and now, whether expressing naked personal neediness or raging at public malfeasance, he’s gutsy, stirring, and altogether convincing. “Babyface really put me through my paces when it came to laying down vocals,” says Stump. “It was tough, too, but that’s okay. We never really learned many musical rules, guitar-wise or vocal-wise, so the opportunity to be schooled by a master was something I wasn’t going to pass up.”

Fall Out Boy doesn’t seem to have a “lead” and “rhythm” guitarist in the traditional sense-do you agree?

Oh, yeah. I still do most of the rhythms, though. What usually happens is, I’ll lay down a basic rhythm part, but because I'm a drummer at heart, I don't play traditional rock rhythms; there's lots of little jagged hooks going on. And then Joe will have these big empty spaces where he’ll lay down tons of guitars and Johnny Marr-type atmospheric parts. You put all that together and it becomes huge; it’s a way bigger sound than if we were playing the same parts together.

Tell me about some of your guitar influences.

First off, I started as a drummer; I never intended to be a guitarist or a singer-things just worked out that way. When I switched to guitar I also had to start singing-it was the only way for me to try to write songs. When I picked up the guitar, I gravitated towards guys like Joe Pass. Now, Joe Pass could certainly play incredibly fast runs, but he had such taste and economy of style -- he didn't always blaze. That’s why I’m probably not a “traditional” guitarist, as you say: I’m holding back; I’m not always blazing. I’m definitely a “less is more” kind of guy.”

And you obviously like Gibson guitars. You play SGs and Les Pauls.

Yeah. Don’t ask me what years or anything, though. I’m real bad with that stuff. But I love Gibsons. For me, they get that “oomph” I need. Every other guitar I’ve tried tends to sound too tinny-tinny and tiny! Gibsons give me a full sound. Plus, I just love the feel of the necks and the way they play so easily. When I’m up there singing and doing my thing onstage, I don’t want a guitar that’s going to fight me.

For Fall Out Boy to achieve such success and sell so many records, especially these days, must feel incredibly validating.

Totally. I remember when Cork Tree came out, we were at the tail end of all those one-dimensional, third-generation rap-rock bands and crappy boy bands. For us to sell a lot of records was validation for being legitimate; that we could write our own songs and play instruments; that we weren’t just some put-together kind of deal; and that we weren’t trying to copy anybody else.

When you recorded Infinity on High, what kind of pressure were you feeling?

There’s always pressure if you want to feel it. But the second you worry about other people’s expectations is the second you can expect failure. Not that we didn't have big hopes for this album-we wanted our fans to love it more than anything. But put it this way: We don’t sit around second-guessing everything. If you do that, you’re bound to make sterile music, and that’s when you can expect failure.

As songwriters, you and Pete seem to operate like Elton John and Bernie Taupin in that you write the music and he pens the lyrics, but you do so independently of each other.

The key is trying to fit Pete's words to my music without changing the words too much, and that can be hard. My usual pattern is this: I sit down with a guitar and I start playing till I find a groove, and the second I hear a hint of a melody I'll grab Pete's lyrics to find something that works. Sometimes there's great lines that just won't fit, and that’s because Pete's a more literary writer than a pop songwriter.

Pete is such a headline-grabber-the naked pictures on the Internet and what-have-you. I know you‘re supportive of him, but do you ever wish he would just cool it?

Not really. The only thing we worry about is Pete spreading himself too thin. He takes on so many projects and gets over-tired. But that other stuff-the tabloid-Internet crap, the naked pictures-I tune it out. It’s not a problem to me.

I’ve heard you say that this record is a response to your naysayers, those who say you’re music is “fluff.”

Seriously, nothing drives me more bonkers! Anybody who knows me knows that I do this because I love it. I have to do it. Our band isn't some prefabricated crap band designed to make money. Believe me, if all I was interested in was money, I would’ve gone into anything else but music.

Some of your new songs musically are more overtly commercial than before. “The Take Over, The Breaks Over,” for example, has a very Classic Rock vibe.

That was the idea. I remember reading an interview with David Bowie where he said, "One day I decided to write a song that sounded like the Rolling Stones"-you know, where the riff is the entire song? And that's how he wrote "Rebel Rebel." I wanted to do the same with "The Take Over.” Classic Rock? Yeah, sure, I guess it is.

At the same time, "This Ain't a Scene, It's an Arms Race" has a great hip-hop beat. You’re all over the map!

Bending genres is very exciting to me. “Arms Race” does have a hip-hop feel, but I still hear it as a punk song. It’s strange: I think we're at a time like in the ’70s. I remember reading about the days when all the arena-rock fans hated disco with a passion. Then New Wave bands like Blondie incorporated disco into their music, totally messing up people's minds; and the trend crossed over to hard rock and suddenly Kiss were using disco beats. That whole notion is exciting to me. If Fall Out Boy can be a genre-defying band, so be it. That’s what we’re aiming for.