The chant of "Two trailer park girls go 'round the outside" is actually a nod to
Malcolm McLaren's Buffalo Gals. The 1981 song is generally regarded as the first commercial rap/scratch/
hip-hop single. It's interesting to note that song somewhat similarly opens with a radio station show intro before developing into an uptempo track with a
square dance caller singing "Two buffalo gals go 'round the outside." Of course, the fusing of hip-hop with square dance never really took off, but the song's influence is tremendous in terms of
mainstream acceptance of hip-hop.
In the context of this song and who is performing it, the chant is just short of genius. Malcolm McLaren did find the NBT but it wouldn't really cash in for at least another decade, and wouldn't be fully accepted into the pop lexicon for two. Eminem validated the white rapper in a way Vanilla Ice never could. His lyric explains it better than I can: "I am the worst thing since Elvis Presley / to do black music so selfishly / and used it to get myself wealthy / Hey! There's a concept that works / Twenty million other white rappers emerge."
Whereas Big Band introduced palatable jazz, and Elvis' rock & roll introduced palatable rhythm & blues, Eminem's pop/rap does so for rap to trailer parks. Vanilla Ice is a joke now and was a novelty then, but Eminem can be and is taken seriously (as much as any pop icon can be). It could be argued, the previous decade's assimilation of sampling methods and rapping into various genres of music is the real sign of Middle America's acceptance of rap. However, I do not feel those two things quintessentially define rap. It's all about the content; identifying in some way with what is said, or at least empathizing (what white college kids did with Public Enemy's It Takes a Nation of Millions to Hold Us Back, I gather) at a bare minimum.
Eminem admits he's doing nothing new. He's merely doing it for a different audience.