(Non-lawyers: (A more-friendly summary.)
A New York City court held that another tenant’s cigarette smoke entering your apartment, given proper severity and assuming that the landlord is uncooperative in eliminating the problem, is a violation of the implied warranty of habitability. This is grounds for a constructive eviction.
It doesn’t directly apply to me, as far as I know, because it was decided in the county and city of New York, which doesn’t include Westchester. Furthermore, I have no interest in taking any legal action — I’d rather just double-pay rent from my move-out date (whenever that happens) until June 30, since that’s likely to be a fairly short timeframe.
But maybe mentioning this to my landlord will get the problem fixed for my last two months here.