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Embarrassing Nickname: The basis of the Professor's mania, hatred and tyranny towards his students is the nickname "Unrat" ("Garbage"), which is completely justified in-universe: he is described as very ugly, disheveled, prematurely aged, rather incompetent and a failure in anything including his own former marriage.
Sleeps with Everyone but You: Rosa is a cheap hooker but she wouldn't be with Ertzum for his whole inheritage. Justified in-universe by the fact Ertzum—despite his aristocratic standing—is extremely stupid and boorish, so stupid he makes the Professor appear brilliant by comparison.