The painful empathetic feeling a man gets in his nuts, while watching another man get a nut shot.
A: *watches someone get sacked in the nuts*
B: *cups balls in pain of watching the poor sap get sacked in the nuts*
C: "hey why are you holding your nuts, you'd didn't get sacked"
B: "I feel it though bro, I'm feeling that nut sack empathy"