Donald Trump supposedly learned a great deal from Roy Cohn, who was a relentless douchebag and all-around horrible human being.
Cohn and Trump were as friendly as any pair of narcissistic sociopaths can get. Cohn was Trump’s personal lawyer and fixer, mobbed-up to his eyeballs, and a total swamp-creature; when Trump was worried that the Russia investigation might be slipping out of his control, he supposedly whined, “Where is my Roy Cohn?” [nyt]
More revealing about Trump, when Cohn died: [wikipedia]
At death, the IRS seized almost everything he had. One of the things that the IRS did not seize was a pair of diamond cuff links, given to him by his client and friend, Donald Trump. The diamond cuff links were later declared to be fake by an appraiser.
Nothing I can write could top that.