Recently a friend was feeling the carbon fiber rocker extension on my ZR1 and stuck a painful splinter in his finger. Afterward we sanded the undersurface of the splitter and rocker extensions with fine sandpaper, making them safer to touch or when I wash my car.
I think they started out smooth, might have scuffed them going over a speed bump or something similar. Mine are smooth on the bottom. But a light sanding occasionally will keep them smooth.