X: I love you, mum.
Me: I love you too, mate.
X: Can I go on the computer?
Me: (Look of incredulity) Are you... forgetting something perhaps?
X: I'm sorry.
Me: (More of the Look)
X: I really am sorry.
Me: For what, exactly? I mean it's really nice to hear from you and everything, but I just want to be clear on this.
X: For being, as you so eloquently phrased it 'A total git'... And oh look you're smiling because it was quite funny- isn't it amazing that I can make you laugh about this?
Me: Yes, your gift is indeed your curse.
X: No, it's not my curse, its-
Me: No, no, no! This really is your curse. You're smart. You're witty. You're fun to be around. And you have NO idea where the line is.
X: See - I think I do know where the line is- I just don't care about crossing over it.
Me: But then this happens - so you need to learn to care. How can we stop things going there? We need a new gesture...
(We used to have a discreet 'You're crossing the line NOW' gesture that I could use on him in company without saying anything, but it backfired on a couple of occasions and lost effectiveness. We spend a ridiculous 60 seconds trying out new gestures, none of which could be used discreetly in the company of other people and one or two that could be construed as mildly offensive in themselves).
Me: None of these are working.
X: Hmmm. I shall need to give this some thought. I'll sleep on it and get back to you.
Me: That would be fantastic.