First, don't bump your threads. If people are interested, they will post, and that will bump them. It's pretty shameless. Also, I hate double posting, and technically it's something that an infraction can be issued for.
Second, I've seen guys do this, but it seems mostly like superstition to me. It doesn't seem to me that a chin is something that can be cultivated, like flexibility or strength. I suppose it's possible, but I'm not sure the brain particularly appreciates it. After all, the brain is an organ, not a muscle, and I'm not sure that the old adage "that which does not destroy me makes me stronger" really applies to the loss of brain cells.
You think it could work like bone hardening? I can punch a brick wall with some force behind it and not really feel it because I've been punching walls for a long time now.
Maybe you just tap your chin and hit it a bit everyday and maybe.. I dunno I'm curious.