In today's Parashat Hashavu'a Chat, I used the qualification "lehavdil" (*) to apply to a pun that jokingly and innocuously related the actions of Datan and Aviram to those of a community member here.
Alex responded to me that "They say that you don't say "lehavdil" between one Jew and another," but later indicated that he doesn't recall where he heard this.
Have you seen a source for this rule?
What is the reason for it?
Does it really mean that we shouldn't use the word to distinguish between a wicked Jewish person and a righteous one? If so, why?
(*) "Lehavdil," literally "to separate," indicates that while two entities may be juxtaposed in conversation, we don't intend to equate them in terms of religious value. For example:
Did ... great rabbinic thinkers of the 1800s ... comment on American slavery and/or the Civil War? (As Dostoevsky did, lehavdil?)