Every culture has its norms, the “dos” and “do nots”, which shape what is not accepted in that society. Then there are gestures, which usually do not mean the same thing from country to country. Other things that can cause conflict are religious rules, and general up bringing we get as children from our parents.
In society we create norms that govern the way we are suppose to live, what should or shouldn’t be done. As you are raised in your culture, you naturally learn those rules and judge others if they don’t follow them. Not really understanding that they might not have been raised in that same society, which generally shape your manners.
For example in the US, we are told as children to eat all of our food to reduce the waste, but in China eating every morsel means that you were not fed enough. In their culture, as a host it is their job to simply provide enough food, since food is much more expensive. So leaving a little food shows that you had enough to satisfy you, but now lets turn it around. In their culture it is perfectly acceptable to speak with your mouth full and even burping, which shows the meal was pleasing. Also, in the Middle East it is not only bad manners to put your feet up, but an insult as well as you would be pointing the soles of you feet at them.