bang your head on the seat in front of you , at its cluelessness , at its idiocy 
(ROOT (S (VP (VB bang) (NP (PRP$ your) (NN head)) (PP (PP (IN on) (NP (NP (DT the) (NN seat)) (PP (IN in) (NP (NP (NN front)) (PP (IN of) (NP (PRP you))))))) (, ,) (PP (IN at) (NP (PRP$ its) (NN cluelessness))) (, ,) (PP (IN at) (NP (PRP$ its) (NN idiocy)))))))
(ROOT (S (VP (VB ) (NP (PRP$ ) (NN )) (PP (PP (IN ) (NP (NP (DT ) (NN )) (PP (IN ) (NP (NP (NN )) (PP (IN ) (NP (PRP ))))))) (, ) (PP (IN ) (NP (PRP$ ) (NN ))) (, ) (PP (IN ) (NP (PRP$ ) (NN )))))))