“I’m jealous of all the people that haven’t met you!”
This just shows that you and your bestfriend know each other well. We’re sure this insult won’t offend you because you know that it’s just one of the things that friends do. Yes, you’re right, insult each other! You are being told that other people are lucky for not knowing or meeting you, and that your friend is unlucky because he knows you, but you know that it’s the other way around. Well, perhaps they mean it when you’ve done something that pisses them off.