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Note that at the time of this post, to the best of my knowledge, there has been no palpable proof that the celebrity was indeed banned from entering China, or that the purported ban is related to him "liking" a post on Twitter. This uncertainty is reflected by a number of online news sources that use such ambiguous words as "says" or "claims" to describe the situation. For all we know it may be a PR stunt, or a less headline-worthy statement that some of his upcoming concerts in China were suddenly canceled unbeknownst to him (which would be a much more believable claim).

Generally speaking, restrictive government regimes tend to be very selective in applying their own laws and policies. As long as you are not the loudest voice in the crowd and don't bring along any South Park (or Winnie the Pooh, for that matter) paraphernalia, you should be fine. (Most likely you will be fine either way, but if you are nervous about the trip, it's best to stay on the safe side.)

No, not yet

Other answers focus on how China is probably not capable of profiling every single person in the world. But digital footprints don't fade - they may not yet be able to generate a profile on you, but that says nothing about their ability to do so in the future. Your tweets, likes, and perhaps ad profile are permanent and outside your control; we must assume they'll be able to tell if you line up with their ideology sometime in the future.

It is also worth bearing in mind that, as soon as you set foot there, they'll be much more likely to be interested in making a profile on you. By crossing the border, you're a lot more relevant to them than the other 80m Germans who haven't visited.

But;

Understand China's goals in doing these things - it's trying to prevent any skepticism of the party from taking root in its populace. The party is not under any impression that the rest of the world is uncritical of it. It doesn't punish just anyone for not being faithful to them; it punishes those who might stir up unrest and threaten the continuity of the party's dominance.

So, if you're going to the middle kingdom to talk politics, they might take offense. But if you're just going to see the Wall and eat some bao, you're going to be fine almost no matter what you've said.

At least, for now.

That was a celebrity and China had a lot to gain from publicly making this statement.

Unless you're a celebrity I doubt they'll ever go through the mountains of online activity you've accumulated over a lifetime (assuming they - or anyone other than the NSA - even have access to all this)

No, I don't think you need to worry at all. I have traveled to China many times over the last 20 years, and I have never been asked any questions at all by anybody in an official capacity. From what I have seen and experienced, the paranoia in Western media is wildly exaggerated. Think of it like this: China wants tourists from the rest of the world, since it makes good, economic sense. They also want to keep the peace, so as long as you behave in a reasonable way, you will not experience any trouble.

On top of that, it is the job of the Chinese Embassy where you apply for visa, to check your background; they are much better placed to look at your background if they so desire - the border guards in the airports have plenty to do, believe you me - they will scan your passport, check your visa and make sure you have filled in the small entry/exit forms, and that's about it.

I think your trip will be certainly secure. In fact, it's too expensive for the China Gov to check whether every foriegners in China to be associated with South Park, Winnie-the-Pooh, or other banned memes which the authorities don't like. If you don't take locations politicaly sensitive in China like Xinjiang or Tibet as your destination, traveling in China is secure and free. HK is still ok for visiting, but it's dangerous to cross the border between China and HK directly because they may ask for investigating your phone, and it's not a good choice to travel in HK for what's happening there.

In fact, the Chinese Authorities focuses on Chinese-own social medias beyond Twitter, Facebook, or Instagram, especially for personal accounts owned by ordinary people. They are far more interested in native Chinese. I mean that you can even bring a Winnie-the-Pool doll to China in extremely security (of course, without association with Xi Jinping). Although monitoring of public opinion has reached a very bad level, and getting worse every day, it's still impossible to monitor everybody in the group of 1.4 billion people. Just enjoy your family trip in China. Have a nice trip!

I will tell you unambiguously: No. If you have a valid visa you will be able to travel to, from and through China with no impediment (with exceptions in Tibet and Xinjiang). You will not face any consequences for liking things on Facebook, Twitter, using a VPN or even making public statements and having discussions about politics. These are in fact normal occurrences for persons in China. As a side note: Winnie the Pooh is not banned.

No one will care.

Last year, I walked all over the Beijing tourist sites (Tienanmen Square, Olympic sports complex, etc.) carrying a book on Free Speech. I had to, because I was reading it for a class. No one even asked me about it.

Before I went, I asked my professor, do you think this will be a problem? She responded by showing me a picture of her standing in a lecture hall in mainland China in front of a giant poster with her name and the words "First Amendment." No one cared about that, she said. They really won't care about whatever book you're reading.

The Chinese Government understands foreigners have their own concerns, culture, likes and dislikes, and it doesn't affect them. Would you ask a Chinese person visiting your country if they liked Mao? Of course not. And they won't ask you if you like South Park, or care if you do.