the_reverend said:

seeps through their cieling info the cellar space below (built on their roof)

Liquids seep.

Cigarettes leave tar and niccotine buildup, which will stink up their apartment, but not yours.

then I waffs up through the carpet, the walls and the kitchen cabinets.
plus, bathroom fans are exhuasts (humidity)

Again, you need air flow for ANYTHING to "waft". Airflow, like a vent, or an exhaust duct that shares an outlet with your neighbor. Smells don't travel like that. A liquid could saturate through apartments and cause a smell, but not cigarettes. Do you have water damage on any of your floors? Wet wood and insulation will carry smells. However, cigarettes on their own will not carry an odor like that.

Listen to Jay, he's absolutely right. Think about mom and dad's house: If there was mildew in the basement, you'd smell it upstairs. However, very rarely would you smell the fabric softener until you were standing next to the laundry.