I knew someone who asked the policeman for directions and he gave them. 

I knew someone who wanted to take a picture with the policeman as he was holding his gun and they let him. 

I saw someone selling food illegally on the streets and trust me you don't want to know what happened there. 

  I nearly got in a fight with an off-duty policeman one night in Guilin. I was drunk and he was hitting on my girlfriend. Fortunately my friends managed to hustle me away, otherwise i'd probably be writing this from back home in England

  Had trouble with the authorities in the visa office once. They saw that I was drawing a line across old visas and considered it akin to peeing on the flag or something. They threatened to put me inside for 11 days but instead sent me to the university where I was studying with a note, believe it or not. The university.........people, read the note and confirmed that, yes, I was indeed a very, very naughty boy, and sent me back to the visa office with a slapped wrist and another note from teacher. I cried and cried really hard into my pillow that night, it was just 'so' unfair.

When I first came to China together with 2 other guys we went to bars the first weekend and one of the others got lost.
He asked the police for directions (he only knew a Starbucks nearby) and the police drove him home.

This is the only trustworthy interaction I know a foreigner had with the police in China.

Almost got ran over twice by cops. Didn't end well for them. Met a few really nice police officers, though. It ended well for them.

No cop has ever asked me for my passport here. I wear suits whenever possible, so they always stop the badly-dressed black guys and demand to see their passports.

Not me, though. Nope. "Hey there, you beautiful white laowai. Why don't you come on over to my house and marry my sister? Listen, we're gonna rough up these Africans and, when we're done, we'd be honored to drink moutai with you."

Little do they know I'm only half white.

There was one black guy dressed in full flava flav white pimp gear, and they left him alone.

Moral of the story? Dress like someone important, and they'll leave you alone. If you dress like a poor person, then don't expect to be treated like the upstanding foreign conquerer that you are.

You can get suits on taobao for less than 500 RMB. Do it.

I had run ins with security guards, have to learn the difference. I'm sure the police watch (us) me. I noticed several times what I am sure were undercover. There was a guy, bigger than me, that would hang around the alley I took. There is nothing in that alley. I am sure he was a cop and watching me. It's not that I'm paranoid. I've also had guys follow me and I'm sure they weren't police.

In 6 years, I was asked for my passport 4 times.  Twice they came to my home, once was at an expat bar (they blocked the doors until they checked everyone's passports, several were carted away) and once was at the entrance to an amusement park.  In each case, the police were friendly, spoke good English and were done in a very short time.  This is why I ALWAYS carried my passport with me in China.

To be honest, I have never had a bad run-in with a police officer in China.  Though, there was one police officer who tried to bring my friend to a mental hospital because he was running through the city center in a red dress.  But when 20 more foreigners (and Chinese) rounded the corner and we all had on our red dresses, the police officer just shrugged and let us all go.

I was drunk and playing with a pug dog. I refused to stop playing with dog. I was arrested and brought to the same rural police station twice in one night. As the town was so small, they took me home both times saying. "Stop Drinking and Petting dog!"

-It was a boring place to live.

I left Guangzhou because I had the police, the PSB, the wanna-be-cops and the tax department showing up at my apartment every two weeks. Hell, they knew my visa and job status, but still they came.

Got fined 50 RMB for being in the lobby of my own building without my passport. Got threatened for deportation for not having my passport on me. Got threatened with deportation by the GZ tax office for trying to pay for the rental tax that my landlord was responsible to pay.

GZ is a terrible place to be considering that if you're polite and friendly with police in China, they're usually extremely polite and accommodating too.

I attended an RTA [road traffic accident in Guangzhou 3 years past. The mother and young son had been hit by a bus while on the zebra/pelican crossing, the mother had been thrown in the air and a came down approximately 10 meters away, I rush to help her but unfortunately the young mother expired in my arms due to sever head injuries. People then guided me to the child around 5 - 6 years of age, he had stopped breathing, after checking his pupils, head, back, leg and arm injuries I checked the airways, a policeman on a motorbike arrive shouting at me to leave the child alone he was dead, the so-called officer never even checked the child so could not have known. He tried to drag me away from the child and we had serious words, telling me that if I did not leave the child alone he would arrest me and take me to court and detention. I informed him that he could arrest me after I had give the child the attention and care that everyone human deserves under these circumstances. Hundreds of people gathered for  the usual telephone video productions, I proceeded to apply the CPR [Cardiopulmonary Resuscitation] after several attempt's the child responded. I wouldn't let him fall into a sleep, by applying nips to his nerve area under the  nose and chest area until the ambulance arrived some 15-20 minutes later.  After they arrived I went to the police and reminded him that everyone has the right to comfort, prayer and medical assistance, I also reminded him that China has the -Good Samaritan law which protects those who help other in need. Still making his threats with outraging anger, He was informed that if he wished to arrest me then he would do do so, or I would see him at the police office the next morning. The local's intervened shouting he was wrong. The young child survived and sometime later came to my home to thank me along with his father and grandparents as also did the police.  

Visa renewal is always a tense moment with many stern words spoken, but it's gone OK so far. My only run-in with authorities is probably too laughable to mention, but here I go: The local shapping mall has a fenced parking area for bikes, and I always lift my little bike over the fence to avoid the busy entrance. One time, a guard starts shouting at me, and I quickly go into the mall and ignore him. Coming out, i see he put my bike outside the fence, though it was undamaged and still locked on the fence. A while later, the guards establish a ticket system, forcing everyone to collect a ticket with them. Then one day i lose my ticket in my shopping bag, and can't hand it back, so I just leave with my bike. A week later, I return to the mall and give them the ticket i lost the previous week. but the guards start demanding a 10yuan fee for losing it in the first place. That's when I say "zai jian", and started parking my bike across the road.

All my experience of police in China have been OK (when they are dealing with me directly I mean, I'va also seen them not give a crap about people have fights right next to them etc). 

They were really good when I got mugged at knife point, and when I was staying with my friend but on a tourist visa, they came around but were again very pleasant and just drew me a map of how to get to the paichusuo. When I turned up they remembered me and gave me a cup of tea while we filled out forms.