L.!.
Surely it would be the right
consequence to send the friends home as soon as he or the friends show disrespect!
However, if you just warn him but don't finally stand to your words he will continue to ignore you.
It seems to me that you are not consistent with your parenting and he is using that to his advantage.
At the next situation I would not warn him but would call immediately the parents of his friends and ask to pick them up! The best effect it will be if they all can hear you.
Send him in is room and do not let him communicate or let him start to negotiate with you to change your mind until his friends have left your home. It is self speaking that he is off the computer for a week.
I am sure that all will take care of the issue. However, he also will start to treat you with more respect.
Give it a try!
Let us know how it worked out.