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Dummkopf = slow, dull witted Idiot = idiot
Fool/Idiot
Ich bin ein Dummkopf translates as I am a fool/an idiot.
The German word for chump is:
Dummkopf
Trottel
Klotz
I don't know, but a dummkopf is dumb head in German if that's what you meant.