What does Luke 22:60 mean?

This is Peter's third, or possibly fourth, denial that he knows Jesus.

In the first, he denies the accusation of the servant girl who let him into Annas's house (John 18:17–18). This may be the same event as recorded in Luke 22:56–57 or it may have occurred earlier. In the second denial Luke records, another servant girl tells the men surrounding the fire that Peter was with Jesus; Peter responds to one of the men who heard her (Luke 22:58; Mark 14:69–70).

This last scenario is the most dangerous for Peter. He is standing around a fire with the guards and servants who arrested Jesus. His challenger isn't a servant girl. It's the cousin of the man whom Peter had attacked in the garden very recently (Luke 22:49–51; John 18:10–11, 26–27).

Peter vowed he would never deny Jesus—that he would rather go to prison or even die (Luke 22:33). Jesus told him to pray that he would keep his word, knowing he wouldn't (Luke 22:34, 45–46). When the mob came to take Jesus, perhaps Peter thought this was his moment. He would show his faithfulness to Jesus. But Jesus didn't fight. In fact, He healed the wounded man's ear and told Peter to stand down.

Malchus's cousin asks Peter directly: "Did I not see you in the garden with him?" (John 18:26). He probably knows exactly who Peter is and what he did. Peter is alone. It's no wonder he denies Jesus one more time.