If you are talking about an object that is used by smokers, then probably the second sentence would be right.
It's a smoker's thing.
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I'm not a teacher
which is a better phrase
1. it is a smoker thing
2. it is a smokers thing
If you are talking about an object that is used by smokers, then probably the second sentence would be right.
It's a smoker's thing.
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I'm not a teacher
I also think the second is true, but It should be smokers' thing, such as an ashtray. Thanks