The 20-year-old Gasi, better known by his nickname Bibi, is the lead singer in a show highlighting the plight of the Roma, one of Eastern Europe's most discriminated-against ethnic groups.
"Gypsy Roma Urban Balkan Beats", starring Bibi and a dozen other Roma youth, tackles the casual racism they encounter in Serbia, a Balkan nation still grappling with the legacy of ultra-nationalist politics and the 1990s' wars that stoked longstanding ethnic tensions.
"How much longer will we take this segregation?" sings Bibi in the Roma language. "We don't ask for much, just a little respect and to be in touch."
The Roma, often called gypsies, a racially charged and outdated term, are an ethnic and often transient group originally from India that has been persecuted for centuries and sent to Nazi death camps in World War II.
Despite laws protecting them in some countries, Roma still face daily discrimination.
"In a bus, I very often meet a group of youth who start insulting me that I am a gypsy," Bibi said. "Even some kids in school that were friendly used to tell me 'You are gypsy, I can't hang around with you, my mum and dad don't let me.'"
At a recent Belgrade performance, singers and dancers from the show -- known by its acronym GRUBB -- challenge the audience about the stereotypes they often face.
"All Roma people are thieves!" reads one message flashed onto a huge screen, as Bibi and his friends ask the audience if they have ever stolen anything.
More than half the people in the theatre sheepishly raise their hands.
"So, it is not only Roma people who are thieves," conclude the amateur actors, who fuse wild hip-hop dance moves and live brass music with traditional Roma songs.
Afterward, 16-year-old Nikola Milovancevic said he felt ashamed.
"When they say how we use expressions like 'You are fighting like gypsies' in everyday speech. We say that without a single thought that it can hurt someone," he said.
The show premiered in Belgrade last May and has since played monthly in the Serbian capital.
Its international success came with a London performance last summer, followed by a show at the Montreal international jazz festival that triggered standing ovations and sell-out performances.
The show is backed by RPoint, a British educational group that holds workshops to teach Roma kids to sing and dance -- but there is a catch.
"They have to go to school regularly and be good students," RPoint spokeswoman Aleksandra Radetic said.
Serbia has one of Europe's largest Roma populations, officially set at about 100,000 though the number is widely thought to be as much as five times higher.
Many, especially those living in slums, have never been registered or have no identity documents.
Few of the 86 percent of Roma who finish mandatory schooling at 14 make it to university level. In Bibi's slum, residents collect scrap metal to make ends meet.
Bibi said in one school he attended nobody wanted to be friends with him or three fellow Roma students.
"They didn't even obey teachers' orders to play sport with us in gym class. It hurt a lot," Bibi said, explaining why he first quit school at age 11.
With RPoint's support, he returned and now hopes to finish high school.
Hundreds of Roma children aged eight to 20 have taken part in RPoint's music classes in Belgrade and Serbia's other two largest cities, Nis and Novi Sad.
But it was only when Canadian theatre director Serge Denoncourt got involved that the project developed into the "GRUBB" show. After working with the kids for three years, Denoncourt said he was overwhelmed by their talent, and by their problems.
"They have dignity but they don't have anything to be proud of, now we have to give them something to be proud of," Denoncourt said.
Apart from plans to return to Montreal, a possible 2012 European and American tour is being discussed. Denoncourt said he is even in negotiations with Broadway.
For its young stars, the show is already changing lives.
Dancer Kristijan Demirovic, who lived in Germany for 12 years, said when he returned to Serbia people "looked at me as if I was from Mars", perhaps because he had developed a more confident attitude.
Performing in the musical has boosted the 18-year-old's self-esteem.
"There is no better feeling than when you see 800 people watching you and applaud," he smiled. "It tops everything."
For Bibi the change is literally concrete.
"Before, I had to move from one slum to another every six months. This year, we plan to move into a real house," he said proudly, as his performance earnings have allowed his family to buy their first property.