Originally Posted by NickB

Whether such a norm exists is an empirical fact. A short string of individual opinions does not constitute etiquette. But a widespread view within a social group of what constitutes socially acceptable or socially unacceptable behaviour does constitute etiquette.

Originally Posted by NickB

I strongly suspect that if you were to ask people whether consumption of smelly food in public transport or similar confined public spaces is socially acceptable or not, the answer would be an overwhelming "no" so I suspect that etiquette does in fact restrict the range of food that it is socially acceptable to consume in confined public spaces.