I always thought it meant something along the lines of “okay, huggy time is over.” When I see it, the hug ends immediately after the back-slap.
I have some space issues, too. Hugging is good, and so are kissing, touching, and the like. I very much enjoy being in someone’s personal space, when I’m invited. I don’t like someone forcing their way in to my space, either.
The reason men do this is because we’re more resonant than women. It’s very satisfying to feel the sub-bass WHUMPH of another man’s torso.
Women have different sized torsos. Most women are thinner than most men. Their resonating chambers are smaller. It’s not nearly as satisfying.
Then again, I find most other things about women’s bodies more satisfying than men’s bodies… 