What is "the fastest thing on two feet," according to a Ray Stevens song?

"The Streak" is a popular country/novelty song written, produced, and sung by Ray Stevens. It was released in March 1974 as the lead single to his album Boogity Boogity. "The Streak" capitalized on the then popular craze of streaking. In 2007 Cledus T. Judd covered "The Streak" on his album "Boogity Boogity - A Tribute to the Comic Genius of Ray Stevens"

Oh yes, they call him the Streak

(Look at that, look at that)

Fastest thing on two feet

(Look at that, look at that)

He's just as proud as he can be

Of his anatomy

He goin' give us a peek

Oh, yes, they call him the Streak

(Look at that, look at that)

He likes to show off his physique

(Look at that, look at that)

If there's an audience to be found

He'll be streakin' around

Invitin' public critique