Our society dictates us how to behave in different situations, at work, in public, in school and how to stay polite when we have a cold or an allergy.
In our cultures it is polite to blow our nose when we have a cold, we use paper tissues our tissues made of silk or cotton to stop our nose from running !
In other cultures however, using tissues to blow our nose is considered dirty ! Indeed the tissue paper is considered as a means to spread bacteria !
You can experience in Asian countries and surely in other countries across the globe that people will use snorting or blow their nose with the hand which is considered in their culture more appropriate.
When we meet such people, especially if we are travelling on a plane our reaction will be to provide them with a tissue. Believe me, if we do that they will not know what to do with it and may use it to wipe off sweat or just use it to dry their hands off after washing their hands.
Moral of the story is we are all conditioned about what is right and what is wrong, however right and wrong are not universal and we need to respect and understand that others have different customs and perceptions !