I don’t like the smell of cigarette smoke, and will go out of my way to avoid people who are smoking in public.
But I’m pretty much indifferent to the smell of cigar smoke, at least until it gets really thick.
It’s been a while since I encountered someone smoking a pipe, but my recollection is that it’s much more similar to cigar smoke than cigarette smoke (though not identical).
So what makes all three of these different from each other?
On a very basic level, manufacturers all use their own individual tobacco blends and sometimes, added flavors. It’s like asking why Coke and Pepsi taste differently. Yes they’re similar and use broadly the same components but each has their own formula.
IMHO, cigar and pipe smoke tends to be hugely more offensive to me than cigarette smoke. It’s all annoyong but cigars will send me fleeing from the room almost instantly.
Previous thread:
As long as I knew him, my grandfather smoked a pipe with cherry flavored tobacco. It was quite pleasant to smell. Both of my parents smoked cigarettes, different brands, and the smell was both horrible. I smoked flavored Tiparillos (thin cigars) for a while in college and the smoke didn’t bother me, but I had an uncle that smoked fat cigars and I couldn’t stand to be in the same room as him. While they are all made from tobacco leaves, they are processed and flavored very differently.
Here is a very good factual explanation from a tobacco company about the varieties of tobacco and differences in processing. This is more detailed and authoritative than what was in the older SDMB thread.