One boy laughs at another wearing an elf hat in the locker room.
People are in the lockerroom.
"One boy" and "another" imply that there are at least 2 people in the locker room, so the boy and another can be simplified just as "people".
exists e2 e1 s1 x1 x2 x3 x4 x5.(n_room(x4) & of(x4,x5) & n_locker(x5) & for(e1,e2) & Theme(e2,x3) & Actor(e2,x1) & v_wear(e2) & in(x3,x4) & n_hat(x3) & a_elf(s1) & Theme(s1,x3) & at(e1,x2) & n_thing(x2) & Actor(e1,x1) & v_laugh(e1) & n_boy(x1) & card_eq_1(x1))
exists p1 x1 x2.(n_lockerroom(x2) & in(x1,x2) & n_people(x1))