Don't know why you referred to 'Nazi'
I'm from Belgium, not Germany but thanks anyway for your information. I'll try to search for it.
Nazis are authoritarians, grammar is a proper rules of speech/writing.
By saying "No, it's not 'dumbfk'" you are implying dumbfk was out of place or inaccurate. You're not only making a double entendre but a false assumption of 'dumbfk' being improper speech by trying to rebuttal it, or at least that's the general assumption when someone makes this sort of derogatory attack.