Mayor Bill de Blasio was greeted with a few jeers as he showed up to help paint a giant Black Lives Matter mural on Fifth Avenue outside Trump Tower on Thursday — with a couple of angry onlookers shouting “douchebag de Blasio” upon his arrival. The mayor joined first lady Chirlane McCray, the Rev. Al Sharpton, Brooklyn Borough President Eric Adams and Rep. Carolyn Maloney (D-NY) to fill in the letter “L” with yellow paint for what some critics, including President Trump himself, have called a political stunt. When he arrived around 11:30 a.m., two or three men shouted “douchebag...