Pumpernickel – From two German words. Pumpern, which translates into “To break wind”. And Nickel, which means “Goblin, devil, rapscallion”.
In other words…pumpernickel means “farting bastard”.
References here, here, here, and here.
This post on the etymology of Pumpernickel has been brought to you by Beano! Beano, for all of you bastards out there.