Reb Shmuel Berenbaum related
A couple of members of lubavitch were passing through the town of Mir in Europe. In Der Mir, the practice was that students did not wear their tzitzis on the outside of their clothes. On of those fellows asked one of the Mir bochrim “where are your tzitzis?” He received the rejoinder “here we don’t wear tzitzis (at all)”
“Why not” was the query.
The immediate quip was Talmudic diction ” ‘k’dei shelo levayesh mi she’ain lo’
[ in order not to embarrass one who doesn’t have]”
postscript
What followed was a public condemnation of the Mir in chabad circles, circulating that the Mirrers do not wear tzitzis.
R’ Shmuel chuckled and said that already in Europe we had trouble from them.