An a unhappy couple sitting at a table in a restaurant.
An unhappy couple waits for their food, which is late.
An unhappy couple could be waiting for their food at someone's home, theater, or another location, not just at a restaurant.  The couple could also just be unhappy due to another reason, so we don't know that their food is late.
exists e1 s1 x1 x2 x3 x4.(a_topic(x1) & at(e1,x3) & in(x3,x4) & n_restaurant(x4) & n_table(x3) & Actor(e1,x2) & v_sit(e1) & (x1 = x2) & n_couple(x1) & a_unhappy(s1) & Theme(s1,x1))
exists s1 s2 x1 x2 x3 x4.(a_topic(x1) & for(x1,x3) & Theme(s2,x4) & a_late(s2) & (x3 = x4) & n_food(x3) & of(x3,x1) & n_thing(x1) & n_wait(x1) & of(x1,x2) & n_couple(x2) & a_unhappy(s1) & Theme(s1,x1))