Interesting, ubiq, that no such medrash actually exists.
So many of the things “someone says” (reminds you af anyone around here?) when you learn growing up, are actually quotes that come from nowhere at all. Then you spend years hearing from men who learned from the real sources what it really says. So thanks for making that clear!
As for Bnei Yisrael’s distinction (or lack of it) in Mitzrayim, they were “metzuyanim sham”. I always understood that as meaning that they did maintain their cultural differences, but picked up some really nasty behaviors from the immoral Mitzrim. If you want to learn it differently, feel free. You certainly don’t want to draw conclusions from some anonymous person on the CR…
sorry for the edit, wasn’t sure if you meant it in the way it came out…