1. Cling film- when the camera flashes it reflects off of the film and blurs the number plate.
2. Builder's foam- the foam expands inside and crushes the camera mechanism.
3. Tyre and fire- place the tyre around the camera and burning is a sure fire way to destroy it.
4. Running it over with a 42 tonne truck- crashing your huge truck into the pole supporting the camera will bend it and stop the camera from functioning
5. Prising it open and removing the film- I think this one speaks for itself.
Some of these may have been urban legends but I have heard of instances where all of these have occurred to cameras in the county at some point or another. I would like to say at this point that I am not condoning the destruction of speed cameras just that you should always try to see the funny side of every situation.