CM, I think you will find most people are happy with the Jerk Festival but not with the odd JERK who attends. In la la land everyone would arrive on cheap public transport and have a wonderful calm litter and violence free day and leave Forest Hill with a glowing feeling.
The reality is that a small number of people do not give a damb about other people and so will park where they damb well please and get shirty if you try and point out the error of there ways.
Roz and others have a point, it may only be one day but why should we have to put up with people behaving like JERKS even for one day?