I am unlucky enough to have had my lungs damaged by pollution from trucks going past my shop in a little Oxfordshire town, while the slip road to the M4 was being resurfaced. (True - I have been in hospital 30 times now as a result). Now if I go into a very smokey atmosphere, it is a danger to me.
I kid myself sometimes that if I stay at one end of a room and someone is smoking at the other end I may be able to stand it. Unfortunately, a lot of smokers are actually chain smokers and the fug builds up really quickly. I then have to leave. In the past, when I have told this to a couple of young guys about to smoke roll-ups in front of me in a very crowded session, they have been really pleasant and gone off for their smoke and returned to the music afterwards.
However, in general, the attitude is "If she can't stand the smoke - she shouldn't be here". 'There but for the grace of God' springs to mind and I can't wait for clean air in English pubs.