Selena Gomez got to perform at KIIS FM’s Jingle Ball on Friday night, but it turned out to be a nightmare for the young singer! Eyewitnesses said that Justin Bieber’s ex was lip-synching when there were sound problems. Then Selena did the unthinkable and said into a live mic, “What the f*ck!” and ran off stage. GASP! But don’t worry, she came back and apologized to her fans for the sound problem, then did a few more songs.