The Art of "Selective Breathing"

I may be able to adjust to the fast pace lifestyle of HK but I don't think I can ever get use to the pollution (i.e. bus fumes, cigarette smoke, bad body odor). My brother said I need to practice the art of "selective breathing". Meaning, do not breathe when an automobile passes by, do not breathe when a person that looks like he/she may have bad body odor passes by, and do not breathe when walking past something that looks like it may smell bad. Well in Hong Kong, that's like 85% of the time! That's why I've been yawning so much. I'm not breathing. It's sad but true.

How do you distinguish someone that might have bad body odor versus someone who doesn't? I don't know. I guess I need to practice that art as well.