One of the first patterns that's usually talked about in phonology is that nasals often assimilate to the place of articulation of a following stop, fricative. So, un-/in- in English is pronounced with a labial nasal [m] before p (impossible, and unbelievable, unless you really stress the prefix there) and with a velar nasal [ŋ] before k (incredible, uncool). But the process is usually limited to /n/, and we don't have problems saying things like Aamco with [mk].
I just heard people on the Stephanie Miller Show mocking Bush for yet another gaffe on the international stage (don't ask — sounds like it involved overflowing foam on his near-beer during a toast), this time in Heiligendamm, Germany. Stephanie Miller repeatedly called him Dummkopf, and it sure sounded like it was pronounced with [ŋk].
It actually works pretty well, since German has the noun Dung, meaning 'manure' (hey, the languages are related!). For yucks, I checked the term and there is actually a placename Dungkopf. Not changing my vacation travel plans to go there, though.