Second hand smoke is considerably less concentrated than first hand smoke. Anybody who's smoked a cigarette can tell you it's a totally different feeling inhaling it directly than it is being near it. Being near it just stinks, inhaling it is .. hard to describe.. maybe painful.
Haha, I knew you'd bring that up!
While this is true, it's still a lot more concentrated than the chemicals emitted by, say, the tar on a road or the exhaust from a car engine. This is again relative to the size of the room and how often you're exposed to it. If it's often (which is generally the only time someone will complain), I think they're going to be a lot worse off than someone who has just been outside and exposed to car exhaust for a while.