A driver in the UK has been convicted of a criminal offence because he flashed his headlights at oncoming cars to warn them of a police trap up ahead. How pathetic, I do it all the time and I'm sure you do too. But the police officer wasn't having it, he said he had 'perverted to course of justice' and he had to go to court. He ended up paying a 175 pound fine, 25 pound costs, plus 15 pound victims surcharge (whatever that is).
Michael Thompson 64, admitted challenging the police officer who would have probably let him off with a warning. The offence of obstructing a police officer carries a maximum sentense of 1,000 pounds and/or 1 month imprisonment. The bottom line here I think is don't be cheeky and keep your mouth shut.