The Undertones slam-bang punk-pop drew its strength from one simple fact: you didn't need a secret handshake to enjoy it. John and Damian O'Neill mated infectious guitar hooks to '60s garage, '70s glam rock, and Feargal Sharkey's signature vocal quaver. Those qualities came together on their breakout hit "Teenage Kicks," whose simplicity harked back to '60s ideals of when the song was king.