I usually wear mine out. Not to "rub-in-the-face", but to show folks that there are Jews who don't fall in the mainstream stereotype of tzitzis wearers who don them and are shomer mitzvos. That said, it's seldom I have my tzitzis hanging down to my knees; usually they're a couple inches below the bottom of my shirt, easy to spot if someone's looking, but just as easy to miss.
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