Justin Bieber did a bit of a moon walk Saturday when the “Boyfriend” singer took the stage at the 15th annual Wango Tango concert for Los Angeles’ 102.7 KISS FM. His sagging jeans reached an all time low. The complete backside of his underwear were in full view when he made a brief cameo appearance to introduce performer Carley Rae Jepsen, a fellow Canadian artist he was instrumental in getting signed to Schoolboy/Interscope Records. See what other superstars played sets. – Billy Johnson Jr.