In 1976, Mandić performed at the BOOM Festival as member of Beogradska Rock Selekcija, an ad-hoc band assembled specifically for the occasion, featuring Robert Nemeček (bass guitar), Zoran Božinović (guitar), Lazar Tošić (drums), Stjepko Gut (trumpet), Jovan Maljoković (saxophone), Ivan Švager (saxophone), and others. That gig brought Mandić his first eccentric episode in public, something he would become known for later on, as he smashed his synthesizer on stage and walked out in the middle of the performance unhappy with the level of commitment his fellow musicians were putting forth.