A friend's Heeler nipped me hard... Left a mark and later a bruise and a hella big blood blister on my calf... He figured I was hurting my friend's daughter (which I wasn't... she was on the trampoline and we were playing around with her mamma right there).
I didn't hold it against him - He was doing his job, and I told my friend so, as he felt he should be mad at the dog for it... But I did finagle an extra piece of pie over it... And it was a fat piece of pie, which was the missus showing her appreciation.
There are extenuating circumstances where nips can be forgiven.
Biting the owner is in a different weight class, as is biting family members, or killing livestock.