Don't "activist" yourself to death
Similarly, I don't say something libertarian every single time someone around me says some ridiculous thing in advocacy of The State or some other form of theft or coercion. While not every moment is a mandatory time to consciously spread libertarianism, I still don't violate ZAP and I don't violate property rights.
I think of it as not littering the world with more statism- there's plenty clogging up the works already.
And, if asked, I don't hesitate to give my opinion (after a disclaimer/warning).