This term is often used by some I know as a kind of joke, not implying its obvious reason. Rather than having references to an actual pimp, it's used to describe something that's cool, in style, or amazes the speaker so much they can't think of anything else to say.
Pimpin is thinkin outside the box........not havein so many gurls on hand thats not pimpin.....so pimpin is just bein you and dont care wat other people think 'bout you!