"The thing you have to remember about the Thong Song is that the basic loop starts with a dissonant chord. (i.e. the music for "Baby make your booty go/ Baby make your booty goooo" sounds much more anxious than the music for "Baby make your booty show/ that thong, tha-thong thong thong.") So the key change is from C# minor to D minor, but the actual cadence moves from C# minor to a G minor 9th, or something like that, which is crunchy as hell."
From a larger article over at