This made me giggle. I have a 5 lb Chihuahua who thinks he is a 100 lb wolf. Sounds like it when he barks, too. It’s always funny when new people come over, they are afraid of the barking beast until they see him 
Anyways, back to why you made me giggle – we play this game with Chili when we are tickling or horseplaying. Whoever is being tickled will cry out “oh, no, Chili! I’m being attacked!” and Chili will rush to their aid. He will nip (which in his case isn’t even so much a ‘nip’ as he puts his open mouth on you, kind of a warning – “I could hurt you if I wanted!” – I am serious when I say I think he sees himself as much bigger than he is!) and will continue “helping” the victim until the “attacker” quits. It’s hilarious.
I will say that we have had a few instances of dominance issues between him and my son. We got Chili when my son was only 3, so they’ve pretty much grown up together so far. Niq (the son) is a very non-violent kind of guy so he has a hard time with the sharp tone needed to back Chili into his place – I usually have to step in if I see Chili acting like he thinks he’s top dog. It’s never anything major, but I refuse to allow it at all.