Year: 2013
Venue: NRJ Music Awards
Was the performance televised? Yes.
Most obviously lip-synched moment? When she shows up on stage, late, with her microphone by her side at 1:03.
By the time Katy Perry started singing live, the damage was already done. The show's host had already stopped the show and asked her to start again because there were some "technical" issues, aka the song started playing before she hit the stage. Whether Katy missed her cue or the show producers screwed up, this is a particularly cringeworthy moment in lip-sync history.