One of the things which LR's teachers brought to our attention was that he seemed to have some difficulty respecting other people's personal space; he tended to put his face very close to another child's face and then didn't understand when the other child got upset. While this is hardly the most dire problem a child could have, it's also not the best way to win friends.
Being a good father, I naturally blamed myself. I have severe myopia and if you look in the dictionary under "coke-bottle glasses" there's my picture. With my glasses off, I'm able to focus on things which are close up very well - okay, my focal point is about two inches in front of my face. Starting when LR was a baby, and continuing all the way up until last year, I used to take off my glasses and come in close to his face where I could see him clearly and kiss him and talk to him and generally be affectionate. I was convinced (and still am to a large extent) that this is why he has a problem understanding personal space; for as long as he can remember, he's been taught to associate having his face very close to someone else's as being affectionate.
Whatever the cause, we felt that this was something we could work on. As with everything else, the best approach to take with him was a verbal one. We began an intensive campaign of "LR, I love you but you're standing too close." We would then stretch out his arm as far as we could and explain "If you can touch me, then you're standing too close." Not perfect, and not true under all circumstances certainly, but overall it works as a pretty good rule of thumb; mostly, it's fairly easy to learn. Over time, he began to get the hang of it. We noticed that we had to tell him this less and less often. He may never truly understand why he needs to do this. But he doesn't have to understand, he just has to do it.
Yesterday, I slipped up a bit. I started to lean over to kiss him and without thinking, took off my glasses, leaned in really close, kissed him on the nose and then looked at him for about two seconds without backing up first.
"Daddy. You're too close!"
Wow. I never thought I would hear him say that.