During the reign of the
Nazis, even though the
Jewish people were legally and socially considered
verboten subhumanoids, it was common for a given Nazi to know one Jew or Jewish family who they considered alright, even while thinking all the rest were scum deserving "
deportation" (really,
destruction). The Jews so receiving such favor quickly unequivocally became known as pet Jews, and such a Jew, if their approving Nazi was in a position of some
power, could even be protected from the worst ravages of the period. Accounts abound (
here are some) of which some of the people who lived due to this status still survive. Naturally, having lived due to such a phenomenon can be source of longstanding conflicting feelings for the survivors.
The phrase remains in use, but modernly is more frequently directed towards Jewish people who align themselves with political ends which have traditionally been hostile to (or, indeed, have substantial factions remaining hostile to) Jews.