I am much the same and will stick for myself when needed etc. But i always try to walk away and ignore people like this, as its just not worth the effort anymore, specially as i have children now. But saying that i did find in the past being overly polite and using the word Sir and Madam for some reason winds them up even more.....
For example once i parked in my local Asda car park that was rather busy for 7:30am, i get out the car and some chav walks up with a bag of shopping what looked like cans of stella and starts to have a go at me because i have parked to close to his car. I look at both cars, i replied with something along the lines of "oh i am so sorry sir, i did not mean to park to close to your car, but if we look at how i have parked my car is in the spot square and even space round the car towards the line. Now lets look at yours sir, its parked all the way to one side. So who can't park their car correctly sir........"
The look on his face was priceless and so confused. Before long he to slung his shopping to the ground and started to give me a world of abuse.... " I replied with something like please watch you language please sir there are women and children present". Now this coming from me, i have a bad habit of swearing to much. The guy then gets up in my face, you know how they can be, so i replied "please Sir, lets see what will happen" he soon stepped back and i walked away saying "have a good day sir."
I must admit i was worried after all this, to come back to my car and find that it had been vandalised or something.