Fig.: an act of betrayal disguised as a gesture of kindness or friendship

My colleague Linda has always been very nice to me, but her friendship turned out to be nothing more than Judas kiss. She knew I was friends with the big boss and wanted to get a recommendation for a promotion

Linda, la mia collega, è sempre stata molto gentile con me, ma la sua amicizia si è rivelata essere soltanto il bacio di Giuda, visto che sapeva che ero amica del capo e lei voleva essere raccomandata per una promozione

Don't pretend to be my friend! Your invitation to this event was just a Judas kiss, as you had already planned to accuse and humiliate me in front of all the guests for the failure of our much-advertised project

Non far finta di essere mio amico. Il tuo invito a questo evento è stato solo il bacio di Giuda, visto che avevi già pianificato di accusarmi e mortificarmi davanti a tutti gli invitati per la non riuscita del nostro tanto declamato progetto

The term refers to the betrayal of Jesus Christ by his disciple, Judas Iscariot, who kissed Jesus as a way of identifying him to those who would arrest and put him to death. According to Matthew (26: 47-50):
47 While he was still speaking, Judas came, one of the twelve, and with him a great crowd with swords and clubs, from the chief priests and the elders of the people. 48 Now the betrayer had given them a sign, saying, “The one I will kiss is the man; seize him.” 49 And he came up to Jesus at once and said, “Greetings, Rabbi!” And he kissed him. 50 Jesus said to him, “Friend, do what you came to do.” Then they came up and laid hands on Jesus and seized him.