For those of you with a background in psychology consider that Pete is the epitomy of Adler's inferiority complex. He is constantly trying to use whatever power he can to upstage "dad" and reaffirm his place in the pecking order. It is obvious that his father never approved of his choice to enter the advertising world and he has been looking for a surrogate father to on the one hand lift him up (Don, Roger, Lane, lest we remember that Roger gave him a second lease on his job in season one and in season 3, Don and Roger came begging Pete to join them) and then on the other for him to "bring them down" and make them feel as small as he does on the inside. For instance, his crude attemps at humiliating Lane this week and Roger the week before (the plane statue unveiling, the reference to Lane as homo, all reeks of phallic symbols and the need to assert himself as "the man."). All this boils down to Pete wishing to be the "big daddy" but he is left feeling like a child. Nothing has ever satisfied him, not Trudy, not his daughter, not even being made a partner. He is always striving to be affirmed and made a "king." The fact he needs to pay a prostitue to do this, when Don (except for one occasion) has never had to pay for women to revel in his charm and looks, only reaffirms Peter's inner longing but outer hatred for Don in the awkward cab ride.
Pete's attempt to win over the impressionable young girl at the driver's ed class suggests a complex dynamic within Pete. He loses out to "handsome" which is clearly a surrogate for Don and every other man in his life that has upstaged him. Notice that Pete looks at his muscles and crotch when "Handsome" is introduced. Pete longs to have "it" whether it be with women, in business, or in his family. He even has a strong reaction to being potentially labeled impotent in season 2 as an insult to his manhood. Even his offspring will long for this father figure, as he is clearly absent (I had not a thing to do with her, in reference to his daughter) from both of his children's lives literally and figuratively. It is the cycle repeating itself. He has no investment in real relationships aside from ones that reaffirm or deny his power and status in life, much like his father's original renunciation of his manhood (calling him a whore in season 2 discussing advertising).
His attempts to literally ovetake and destroy "dad" have all ended in failure as well. His ttempt to blackmail Don, his attempt to take out Roger (who in a way has become more invested in his work than ever, at least for him), and literally being beaten up by Lane. When Pete says he "has nothing" at the end of the episode I believe he means he "is" nothing. He is not a man. He is a child who cannot even figure out his own plumbing. Much like the reference to Beethoven in Kosgrove's story, he lacks the ability to utilize his tools and is left fumbling in the dark alone and scared.
I have way too much free time at work. sorry if this was boring to you guys and I do not blame you in the slightest for not reading it.