Critical mass doos and donts?

I think the hundreds of dickheads who ride on pavements, straight through pedestrian crossings and the like, day in, day out do far more to harm the "cause" of cycling in London than a motley collection of crusties, trustifarians, reinsurance lawyers and lycra clad pony tailed Germans riding slowly around central London once a month.

Like the surrounding of motorists, jumping on bonnets, vandalising of cars, swearing and offering out for a fight. Yeah they love it, them drivers.
Not sure how common this is but I could never do a CM after those scenes.