mook jong man
Senior Master
Since we're talking about upper cuts to the head and/or body, I'll toss out the arm pit. After a gross motor skill deflection or a trap or from a grapple an upper cut into the arm pit (particularly using a knuckle punch) can do wonders to cease hostilities from someone. Done hard/fast enough it can damage the shoulder and facilitate a lock or throw quite nicely.
The arm pit is a vital spot
There is a technique in Wing Chun where we side parry the opponents straight punch and we shift to the side and side slash up into the arm pit area with the edge of our hand.
It is very painful and it can feel like your whole arm has been paralysed.