Someone riding sideways on a motorcycle.
A motorcycle rider is showing off.
riding  doesn't always mean showing off.
exists e1 x1 x2.(on(e1,x2) & n_motorcycle(x2) & Actor(e1,x1) & v_sideway(e1) & n_riding(x1))
exists e1 s1 x1 x2.(a_off(s1) & Manner(e1,s1) & Actor(e1,x1) & v_show(e1) & n_rider(x1) & of(x1,x2) & n_motorcycle(x2))