N2,
If it adversely affects the FO on the flightdeck then it is a flight safety problem as well as a totally unnecessary health hazard.
The RAF used to have a policy on the Puma that the cockpit crew were allowed to smoke IF there was an ashtray in the cockpit. It got to the stage where the aircraft used to stink and sometimes when the cockpit windows were opened in flight there used to be a blinding flurry of fag-ash. (There was no other ventilation apart from one punkah louvre powered by the forward airflow - not good in 38 degrees C and 98% humidity).
The ashtrays were removable. In Belize we used to have a few chain smokers. Not surprisingly the ashtrays often disappeared without trace. The chain smokers quickly found the manufacturer's part number and persuaded the supply officer to order more. It became a war of attrition and the jungles of Belize are now littered with the damn things, especially the first leg of the day from APC to Punta Gorda. The non-smokers eventually won but I for one always wonder if I ever clouted anyone below...