the off-center humor is a constant 
(ROOT (S (NP (DT the) (NML (PP (IN off) (HYPH -) (NP (NN center)))) (NN humor)) (VP (VBZ is) (NP (DT a) (NN constant)))))
(ROOT (S (NP (DT ) (NML (PP (IN ) (HYPH ) (NP (NN )))) (NN )) (VP (VBZ ) (NP (DT ) (NN )))))