Do Not Blow Your Nose In Public; It Is Offensive
In some cultures, blowing one’s nose in public is ok. This is not the case in Japan, as it is seen as offensive. The whole process is not only disgusting – but it is highly frowned upon for someone to blow their nose if they spit or perform any mucus-producing bodily function in public, for that matter.
If an individual MUST perform any of these actions, they have to find a way to prevent others from seeing/hearing it go down. You will not be surprised if you hear a person sniffing until they get to a more private setting where they can take care of the situation. In this case, discretion is always warranted.