The Russian word used is a relatively mild term of abuse for a slow-witted or foolish person, and could also be translated as "loser," "dumb-ass," or "chump". The vandals did not, however, leave any accompanying critique of Kant's thinking to justify the smear on his intellectual powers.I asked a Russian-speaking comrade about this, and he tells me that the actual word needs context. It's apparently a term that is of particular origin in the criminal community in Russia, which thinks of itself as pursuing a life worthy of a man because it isn't subordinate or groveling. This term refers to someone who deserves to be robbed, because they are the kind of person who slaves away to pay taxes and be lived-off by others.
Thus, the proper translation is more like "Kant is a sucker," which is much more defensible than him being a moron -- or even "Kant is a square," which is actually true. Kant is the squarest of squares.