How hair guru Sandy Poirier turned a nondescript warehouse in Southie into the hottest salon in the city

In the four years since, Poirier has turned Shag into the hottest salon in the city and established himself as the most ambitious - or at least the most relentless - man in the Boston hair business. Outspoken, mightily tattooed, unapologetically self-promoting, Poirier’s about as far from the cool restraint of Newbury Street as you can get. Yet in a city still famous for its reserve, his bad boy act is working. This year, Poirier expanded Shag to 5,000 square feet, more than twice the size of the original. Twenty-three employees see as many as 100 clients a day.

“Sandy is certainly one of the biggest personalities in Boston beauty,’’ said William George, whose local mini-chain, James Joseph, has four locations, including two on Newbury Street. “He understands the performance aspect of the hair industry better than anyone else. Clients come to be entertained, as well as to be beautiful.’’

And entertained they are: Shag is the only salon in town with a permanent disco ball, club lights, and DJ setup. “I want the place to be more than just a salon,’’ Poirier said. “Salons are tacky.’’ A disco ball, it would seem, is not.

A self-described ADD sufferer, Poirier has some of the fastest shears in town, which allow him to see an average of three clients an hour even when his distractedness can take him away from the chair several times during a cut. One Saturday in October, he welcomed a new client, a conservative-looking IBM exec who’d flown in from North Carolina for the sole purpose of having her hair “shagged.’’ This, said Poirier, isn’t unusual. He’s become known for being able to rebrand a head of hair with little direction and good-to-great results. Few stylists in Boston can truly do this, and those who can - notably Jeffrey Dauksevich of Umi and street legend Dean Mellen, currently at Patrice Vinci - charge considerably more than Poirier’s $80. (Other Shag stylists charge $40 to $75.)

“I wouldn’t know where to begin to charge that much,’’ Poirier said of Dauksevich’s $400 fee. “I just can’t do that to people.’’

Unlike Dauksevich or Mellen, however, many of Poirier’s cuts are Hollywood-derived: recent favorites include the Kristen Stewart mullet, the Jessica Alba bang. When “Factory Girl’’ came out, Shag stylists learned to re-create Sienna Miller’s Edie Sedgwick pixie. Occasionally, Poirier will post a how-to on YouTube. His demo of the Alba bang cut generated more than 22,000 views.

Indeed, the camera loves Poirier; his exaggerated looks and say-anything approach make for great TV. In the last few years, his salon has been featured on MTV’s “Made,’’ the Style Network’s “Split Ends,’’ TLC shows “Makeover Train’’ and “Miami Ink,’’ and, most recently, Animal Planet’s “Superfetch,’’ in which Poirier’s French bulldog, Chloe, learned how to retrieve and deliver a smock. Poirier doesn’t have a publicist, relying exclusively on word of mouth and his side job as a DJ to bring in new business. He obsessively logs hours at the computer - Facebooking, tweeting, and, soon, blogging. After giving the IBM exec a new asymmetrical cut, Poirier sends her away with a Shag sticker and reminds her to watch “Superfetch’’ that night.

While Poirier is flamboyant - he likes being the loudest guy in the room - his motivation seems to stem less from a desire for money or fame than from a basic desire to please, bad attitude aside. When he’s not being cocky, he’s genuinely self-deprecating, and regularly turns to clients like Herb Chambers and local restaurateur Ed Kane for business advice. The rules he sets for his staff are few, but important: No gum chewing. No smoking during working hours. No cheap shoes.

“Some people interview, and I wouldn’t even let them watch my dogs,’’ said Poirier. Those he does hire stick around. “It’s not like selling T-shirts,’’ he said. “These kids are artists. I know when I was their age, I didn’t want to be told what to do.’’ So he doesn’t.

Poirier’s carefully cultivated look - what one pal calls “a hobby in its own right’’ - is that of a stylish biker badass: multiple piercings, blended tattoos, painful-looking ear decor. He favors head-covering bandanas or studded baseball hats, but what he lacks in coif, he more than makes up for in facial hair. His trademark beard is a long goatee, dyed black. On bad hair days, he’ll wear it in a braid.

“I always liked Sandy because he never apologized for who he was,’’ said Umi’s Dauksevich, who worked with Poirier in the ’90s at a Newbury Street salon called Eco Centrix. “Whatever point he was in his career, he always believed he was the best damn thing there was, and if you tell the world you’re the best, there are many people who will believe you.’’

Growing up in North Providence, where his dad owned a gas station, Poirier got into hairdressing to meet women, plain and simple. “A hairdresser friend was the guy who always had hot girls and cool cars,’’ said Poirier, who now drives a Porsche Cayenne with the not-so-subtle license plate 6969. “I’m not good at school and I’m not good at structure. But at hairdressing school, I was the only guy in the class - which had its advantages.’’

Like many creative types, Poirier has a love-hate relationship with Boston. He’s a local guy, dropped Rs and all, yet he can’t help but feel betrayed sometimes. And bored. At 40, he’s never been married.

“Girls here want the 6-foot-tall guy in the finance business who wears his Red Sox hat backward,’’ he said. “And if they don’t, they’ll go out with me for a little while and get nervous and go back to their old loser boyfriend.

“I’m not safe. They call me later and say, ‘Sandy, I made a mistake.’ ’’ He shakes his head.

He now lives in Quincy, where he can keep his car, motorcycles, and mountain bikes under cover and his dogs have room to run. Someday, he thinks, he’ll take Shag to New York or LA, but not yet.

“It’s like politics. Politics is local. Hair is local. Look at Mizu,’’ Poirier said, referring to the chic salon at the Mandarin Oriental, “thinking they’re gonna change the world. It didn’t work. The kids at James Joseph quit to go across the street and charge $25 more. They don’t get any better walking across the street. I don’t want to kid myself into thinking I’m ready for something I’m not. We’re close. I still have to do a little more groundwork here.’’ (George, for his part, said that James Joseph’s turnover is actually extremely low.)

That groundwork includes his sideline gig as a DJ at the Dom Perignon lounge at Bond in the Langham Hotel, playing mashed up versions of electro-trance and pop. “I have ADD bad,’’ he said. “That’s why I love to DJ. It gets me to a place where I can focus on one thing.’’