[aflag]

Criticising the police is unlikely to get you in jail. Theoretically he was arrested for impersonating the police, which is a crime. It's just that when it's a clear parody, then it's not illegal. That is a bit nuanced, though. And you can see how some officer may get that wrong. By the way, now that this has been tried, it's extremely unlikely you will be arrested or investigating for creating a parody page in Facebook. At this point, they would lose in court if sued for wrongly arresting someone that did this exact same thing.

Anyway, if you do things that are in the boundaries of the law, you shouldn't be surprised if you get arrested.