Today I have learned that in Japan blowing your nose in public is very rude.
I agree that it can be not a pleasure. So what? What the person who has runny nose should do it the public place, it is not something that he or she can manage.
How about it in your culture?
Japanese, is it true? What do you do when you have a runny nose?
For Brazilians this is also a very rude attitude and many of us get shocked once we travel to Europe and find out that this is the most normal thing for Europeans. When I was travelling in Europe with my mum, she would get horrified with people blowing their nose with no mercy anywhere at anytime :D I remember we were travelling to Czech Republic on a train and there were some Germans sitting next to us and they would constantly blow their nose, very loudly and my mum would look at me speechless. Also in some restaurants, by the table we would constantly hear it.
Generally speaking, Brazilians tend to be very discreet, go to the toilet and close the door so no one has to hear you blowing it, of course in some situations you cannot help but really blowing it but if we can avoid it and be as discreet as possible, we will.
I would say in the U.S., as long as you wash your hands after you blow your nose, no will think you're rude in most cases. However, at the dinner table or at a restaurant, it would probably be better to excuse yourself and go to the restroom if you can. If you have a runny or stuffy nose, people would prefer that you use a tissue and just take care of it than to keep sniffling.
I remember riding on the trains in Japan and walking around the city, and I rarely saw anyone even wipe their nose with a tissue. I will say I never heard anyone blow their nose loudly, but I would see people wipe their nose. Yes, it's gross, but I think it's more about causing a disturbance, and people don't want to disturb others. At ramen restaurants (at least in Sapporo), there are boxes of tissues for the customers because if customers order a spicy dish, their noses get runny. I never hesitated to use a tissue in public if I needed to, but I at least avoided blowing loudly to avoid causing too much of a disturbance.
It isn't considered to be rude in the US. Perhaps mildly disgusting. But not rude.