The term is derived from the motion in which you would drive over a speed bump. You slow down to check out said person and upon discovering how unattractive they really are you resume speed and continue on course.
The opposite of a Stopsign
Joe: Yo, that girl is phat to death.
Rick: Yeah, lemme catch up to her before I try to holla.
"Rick and Joe catch up and continue to walk past"
The frustration and anxiety typically associated with traffic speed bumps is included, especially if one has an impending bowel movement.
"That queer really left a reservoir of Santorum in my ass after that speed bump."