Sometimes you need to reason with people in a calm and rational manner. Other times you just need to punch them in the face.
There’s an old skit with Shaun Micallef and Diana Reid, which was done shortly after they got rid of the 1c and 2c coins. In it, Shaun goes upto a petrol pump and takes out 2c worth of petrol. Goes in to pay, and confirms with Diana (the petrol station attendant) that, rounded down, he needs to pay nothing. Then he walks his car to the next pump and proceeds to do the same.
At this point, Diana pops her head out of the shop door and yells “Piss off ya dickhead”.
In other countries, you may have to defend the ridiculous technicalities and appeals to authority. In Australia, I believe you should be able to say “Piss off ya dickhead”.