When traveling to motorcycle shows and exhibitions, I often like to ask chopper builders what inspires them in achieving the S-shape defined by the gas tank, seat and rear fender. In the majority of cases (when the wife isn’t around), the answer is that the source of inspiration is a woman’s body.
I believe that this picture reflects that very well.
P.S. Note that the woman is wearing tanga underwear just so that almost nothing would stand in between her and the bike. Looks like a perfect blend to me!