Kiss of Judas: "According to the Synoptic Gospels, Judas identified Jesus to the soldiers by means of a kiss. This is the kiss of Judas, also known (especially in art) as the Betrayal of Christ, which occurs in the Garden of Gethsemane after the Last Supper, and leads directly to the arrest of Jesus by the police force of the Sanhedrin (Kilgallen 271).
More broadly, a Judas kiss may refer to 'an act appearing to be an act of friendship, which is in fact harmful to the recipient.'"