One of the most unbearable flights was with Emirates in late 1990s to Philippines, flying in non smoking and smoking seats started in the row behind. Had to ask to be moved after just 10 minutes as I couldn't breathe sitting in a thick fog of smoke with a child and felt really ill ........... Emirates upgraded us to business class on the return flight

Also KLM, Amsterdam to Kuala Lumpur ....... the guy next to me smelt SO BAD I was sick and moved again ......