My eldest brought 3 uni mates home for the weekend. I realised they all greeted me differently. Lad one gave a formal handshake, lad 2 raised hand in a wave and said hi, lad 3 hugged me. All those greetings seemed right at the time (they all arrived individually) I now can’t think which would be the correct way to greet them - a handshake I guess but seems a bit formal for 20 year old lads.