An acceptable behaviour contract (ABC) is an agreement between you and the police that you will refrain from acting like a complete tosser in public. Whatever you choose to do in the privacy of your own home is, at present still up to you, but when out and about, you agree to maintain a standard of demeanour that does not constitute civil disorder. The police make no such reciprocal undertaking. This is only to be expected as they are there to diffuse public affray wherever it occurs and this can require quite a bit of violence in order for them to achieve full job satisfaction.
Cartoon from www.magazine.concordia.ca