In addition to PC #1's good suggestions, I would recommend you check your co-op's House Rules for a no-smoking clause. One might have been added recently, although as a shareholder you should have been notified at the time.

Co-ops and condos must abide by a Warranty of Habitability. This is law which states in effect that in multi-unit buildings, it is the responsibility of the landlord (or co-op board or HOA) to insure each unit is habitable. You should check the Warranty of Habitability for Westchester to understand exactly what it says.

Second-hand smoke of any sort is the major habitability complaint. It sounds like in the building you visited, everyone was cool with the marijuana smoke so no one complained. In the building housing your sublet unit, some shareholders are not so understanding. But they will most likely prevail if this becomes a legal matter.

I don't think you or your sublet are being targeted. The fact your sublet smoked a second time after being warned affects his credibility. If a unit owner once again smells MJ smoke, it is not too difficult for them to arrange with a board member to visit the unit owner's apartment while the MJ odors are present. The board also has the right to enter your sublet's apartment at the same moment in time to sniff for tell-tail traces of MJ smoke.

The best thing you can do is warn your sublet against smoking anything. Period. Then be proactive. Notify the board that if they receive another complaint, you would like a board member to immediately visit your unit to see if any aromas are present. Incense and other aromatics will only decrease credibility further.

Please be aware that I am not an attorney, and what I wrote above is worth what you paid for them.