ya, its better to be prepared then get jumped and get your ass kicked. I've been in fights where the guy doesn't give you a chance to say no. Like I said earlier. I got in a shouting match with this guy and it started getting out of hand. I said "Whatever" and started to walk away. As soon as I turned my back he clocked me. I turned around to flying fists. If I hadn't fought back he woulda hurt me. I managed to get the best of a scramble and I held him down by his throat and got him in the full mount. From here I could just pick my shots until he gave up. The point is that I coulda yelled "NO! I DON'T WANNA FIGHT!" But to him that would just mean he could beat me up with out me fighting back. He was determined to hurt me and my only option was to fight. I, unfortunatley, ended up paying some small medical expenses and a $250 fine.
So to avoid all this trouble try as hard as you can to keep yourself away from these kind of people. Even if you win you could loose (via legal penalties). But if you have to fight its better to know how.