Mandarin Chinese is an incredibly complex language. Not only does every word have a different character for each and every word in the traditional written form, it also has a lot of homophones—words that sound similar but have different meanings. Because this was hard to learn, sometime in the mid-20th century there was an alternative called Pinyin that was developed to simplify the written form of homophones by grouping them all together. Unfortunately, GAN4, one of several “gan”, means “f**k”, while GAN1 means, “dried” and is commonly used in grocery stores. The plausible explanation for why China is just so rude is that store owners are using a very poor translation system that automatically translates GAN4 for every use of the character Gan. So, there you have it, another explanation as to why Chinese signs curse so much.
Image credit: THE ETIOLOGY AND ELABORATION OF A FLAGRANT MISTRANSLATION by Victor Mair posted on the Language Log.