You can't convince him. You can tell him and your reasons for thinking he is not a good friend but ultimatly he must make up his mind.
Suggestion: Convince them to do something more fun to them then runescape.
He gives him chocolate
you tell them to join
say please
What arguments would you use to convince a friend that the lives of human beings are dependent on solar energy?
Your friend is going to see what they want to see; so all you can do is try to convince him the best you can. If he doesn't see what you see then you will just have to let him come around to it on his own.
motivate the importance of that particular download
It didn't take much to convince the jury.How can I convince you to come on a date?
Janette is trying to convince Richard to let her play in the baseball team.
Beg them not to and talk to their parents.
tell them u will pay them or do a chore for them.