Here’s a great story: I was in shul a few weeks ago, and one of the hanging straps on my Shel Rosh was turned around, so the black side was not facing out. A guy in shul came over to me and turned it around, thinking he was saving me from a certain harsh Gehennom sentence.
Unlike him, I actually learned hilchos tefillin, so I decided to have some fun, instead of just ignoring him. (It was probably not the bein adam la’chaveiro approach.)
I feigned ignorance, and asked him what was wrong with my tefillin. He answered that the black side has to be facing outwards. I said ok, let’s go check it up.
So we opened up a Mishna Berurah (Siman 27, S”k 38) where he says that the only part which needs to have the black facing outwards is the part around the head, and the first wrap around the arm. About the part which hangs down from the Shel Rosh, however, he says “??? ???? ?????? ???” – one does not need to be careful at all.
At this point, he should have apologized and said, “I’m sorry; in the future, I’ll try not to correct people on things which I do not know the halacha about.”
But he didn’t.
He pointed to the next line in the Mishna Berurah (which I knew about), which says “???? ???? ??? ????? ???? ????? ????? ????? ??? ??? ????? ??????” – However, because of “noi mitzvah” – making a mitzvah beautiful – it is proper to flip [the strap] so that the black [side] should be facing outwards, even on the extra [part which hangs down].
Excitedly, he showed me that he was right! The Mishna Berurah does in fact say that because of noi mitzvah it is proper!
Note that he does not use the expression “hiddur mitzvah”; he says “noi mitzvah”.
I asked him, “Do you also run around town putting up decorations in everyone’s sukkah?”
That shut him up.