ass bombs are what i thought of right away. incessant hacking and spewing of phlegmballs might be equally offensive.
once, i was in restaraunt, and a guy near me lit a cigar. i was a little down on my health and the cigar smoke really bothered me. i had several couging fits that i tried my damnedest to keep local. soon, though, it was obvious that i was being disruptive. the fat *enter colorful word* and his family actually gave ME dirty looks, and other reatsraunt patrons snickered and whispered while pointing at me. no one thought for a second about the dude and his cigar, but shame on me for being discomforted by toxic air.
back to the topic at hand; i think i'm with sean in that it might be easier to learn to tolerate people's habit (no matter how stupid it is) and take it upon yourself to avoid situations that put at unwarranted risk. perhaps our absence will spark some enlightnement. if not, then at least you're not near.
getting to that point might be tough, though. in the mean time, the mask might be poignant. just be sure to wear it everywhere it might draw attention. the car, the dinner table, the living room etc. i know it might take some getting used to, but the statement alone would be worth it.
good luck to ya!!