I have 4 boys, and a girl. My girl, I don't worry about, she's quick with words, and that's how they do it. She also has 4 older brothers, nuff said.
My boys all know the rule, never hit first, always hit back.
The second youngest is a middle schooler, very mild tempered, nice kid. He got poked at a few times for his trouble in going out of his way to be nice. I told him that the next time some kid walked past and hit him in the head, turn and punch them in the mouth. Being a good kid, he did what he was told. School called, I explained the situation, and it all worked out. I took him for a treat after school, for manning up, and he hasn't had a problem since.
The younger boys have had no real problems, my high schooler has had a few after school meetups, and seems to be no worse the wear for it. He has learned to pick his battles though.