They usually don't even know how much they stink, and not just when they are actually holding a lit cigarette. The smell absorbs into their clothes and hair (not to mention their homes and furniture) so they usually smell like dirty ashtrays, but they are so used to the odor that they aren't aware of it.
If they are actually smoking the smoke can be smelled at least ten, and often twenty, feet away even though it's only visible within a few feet and the smell lingers after they leave the area.
People with breathing problems are usually careful to hold their breaths and walk quickly past places where they know smokers tend to congregate, but it isn't easy to guess everywhere the poison fumes will be found.
If smokers drive with open car windows the smoke usually bothers people driving behind them even if they don't have serious health problems.
And, as most people know, smoking can cause serious disabilities. My stepfather had emphysema so I saw how dangerous the results can be.
In a way, smoking is a disability itself. It's an addiction and, like most addictions, seriously limits the lives of those who have it. If you question that statement just watch what happens if a serious smoker goes without nicotine for a day or two.
People I know who are in recovery from illegal drugs and alcohol say stopping smoking was far more difficult than giving up the other addictive substances.
But, as my friends have proven, it can be done, and by freeing themselves from smoking they've also stopped endangering and offending many other people.
Smoking stinks, but there is hope.