Associate
Have a word, say you don't mind them smoking weed if it is really them, but would prefer they close their bathroom door when they do so the smell doesn't come up through the vents.
Would bother, you might get on the wrong side of one of the weed smokers what's there.
An annoying situation, though...
I think a knock on the door and a polite request, or a quick note under the door would be my first step.
Weed is one of the most horrific things i've ever had the misfortune of smelling.
4. Tell the Feds a Colombian cartel has moved in below you = Guns Cops Gas Stamping all that good stuff Hippys don't like.