I observe from this scene that Slavi changes his position throughout the conversation. I.e., he is saying/doing something on one occasion, and on the next occasion, totally saying/doing something else that negates his previous speech/gesture.
If you watch the video, once he was saying he didn't know the girl, then he asked her name and mentioned her age; once he said McCall insults him, next he said he was fucking with him; Once he gave his hand for a handshake, next, he threatens and makes fun of McCall. I.e., the character is full of unpredictability.
Why was that?
What did the screenwriter want to achieve by that? Do real-life mafias behave this way?