I agree that I can't blame him totally for lashing out for the above reasons, but still does not make it acceptable behavior. He did bite my wife's sisters leg when she stepped on his toes and did not get her foot off his foot right away-poor guy screamed really loud then bit her (-lesson learned-he stays in his crate when people are over). He tends to walk by your side, right next to you, so it happens frequently, but not if you appoligize the instant it happens.
However we can minimize most of what pushes his red zone buttons, but like stepping on his toes, him getting hurt or getting his nails trimmed (at the vet) just can't be foreseen or avoided.
I might also add that trimming his nails did not allows go so bad, but just increased over the 7 years (and we never trimmed them too short-bleeding) We used to be able to do it our selfs once in a while, then we went to groomer and he was OK, but slowly, he decided he was not going to have none of it from anyone for the most part - although he did let a Vet assistant trim them, the next visit he goes psycho?
You just don't know how he's going to react from one time to next, or with certain people.
Also these are smart dogs, what works one time (muzzle etc> ) he learns to avoid the next or he's just sees it and wont let you get near him. Also he learned if his sticks his head between his front legs you can't get a muzzle on and your too afraid, and vulnerable to get bit, to reach under him near his mouth.