I got searched a lot by customs in Seattle on my trips from Beijing when I started working there. I think they were looking for pirated DVDs or something; joke was on them since my bag was always mostly empty coming to the USA (I would fill it up coming back since shopping in the states was much cheaper than in China). They weren’t rude though, I found it just annoying to be searched.

Chinese police...well, I mean, there is crap you have to put up with as a foreigner. Finding the right amount of paper work to register at the local PSB (and sometimes needing to drag your landlord along), and having to re-register after a foreign trip. Then the random checks when they come to your apartment to check your paper work... Chinese police aren’t bad by any means, but if you are a foreigner living in China, there will be some friction.