what makes me shiver with this story is that the guy for all we know could have aids or something and spitting in the guys face could get in his eyes.
I am not good with politics but do you remember the guy that hit that other guy(politic) with an egg, the camera turned to him and he stood there smirking like hell with his arms folded so chuffed with himself, then the politic turned and smacked him, wipped the smirk right off his face.
I dont think that was unproffessional, and he is representing out country, I think he had every right to land one on him.
As for the fiver thing, I would have siad no the agreement was £10 in and out, if he didn't want to pay, invoice him. I did that with a residential customer once. She asked me to clean her windows as her other windy hasn't been by for ages, so I did, and booked her in the next month. Went by the enxt month, and she waited until I got to the last window, and popped her head out, it was a different woman from last time. "Your not doing ours are you". "Yes I spoke to mrs blah blah last month and she requested the service", she said "no the guy was here yesterday", "that wasn't anyone from my company, if you have asked two window cleaners to clean your windows and not canceled one thats you fault. I have cleaned your windows as requested last month", "Well I am not paying for them to be cleaned twice", I said "If you dont pay, I will have to invoice you, and someone will be out to collect it", "fine do that", so I came back with an invoice knocked her door, handed it to her and reminded her someone would be back. Went back that night and got me money,then imeadiately dropped her.
I think you lost it when you ripped the tenner, and that agrevated the situation, but he knew what he was doing, if its a shop, he had change. If he honestly though you agreed £5 then he would have handed you a fiver, or five coins not a tenner. So he was definately at it, he knew what he was doing, so I wouldnt say you were completely unjust in your response. But the minute he spit at you, he crossed the line, and think you have every right to hit him.