The humor in this meme could likely arise from the visual trickery involved. The angle of the photograph creates an unintentional optical illusion where it appears, at first glance, that the person on the bicycle has an unusually long arm extending to scratch their leg. The reality is that there is another person standing behind the cyclist, and it's their arm that is visible. The humor comes from the double-take or realization moment as viewers understand the visual misdirection.