God I remember that finger. Pushing, poking, driving.
I don't recall it on my breastbone, but I do where my shoulder connects to my body.... that little soft area under the clavicle.
Ouch.
Wow... just thinking about it gives me the chills.
But I always hoped that one day someone was going to see it coming and use a textbook as a shield. In my imagination, I saw the finger just go right through the book and STILL poke the kid.