Don't worry about a lawsuit. Even if this guy gets lung cancer.
First he would have to prove that his lung cancer was brought on by the second hand smoke from a different apartment. If he could prove that, I want him to sell the Brooklyn Bridge for me.
Second, he would have to find an attorney that would take the case on a contingency fee agreement. Or fork over a ton of money to even have the lawyer file for the suit.
Those two things are two very, very big hurdles to climb.

