Heres something I was told recently, by someone who builds passenger aircraft......
Smoking in an airliner makes the air cleaner!
The reasoning behind this is that when people used to smoke on an aircraft, the airline had to keep the air free from smoke, (due to some technical issue
) so they needed to filter the air in the cabin with a higher amount of 'fresh air' at a higher rate.
Now, because there isn't smoke in the air, they use less 'fresh air' in the cabin than before (due to cost).
This has resulted in the traces of carbon monoxide being higher than before (albeit, within 'legal' levels) and therefore their is more aggresive behaviour on more flights (especailly worsened when mixed with alcohol)
As Walter Sobchak said; "I did not know that"