Bo Dietl is a moron. That is why it was funny. De Blasio was even being ridiculed by him, and Dietl, who usually struggles to sound coherent, had him pegged really well.
And De Blasio has done little right in his first year. He campaigned on meaningless rhetoric -- some of it divisive. Few people were paying attention, so it largely got ignored. He got into office and immediately got smacked down by Andrew Cuomo over his school ideas, and since it's been one gaffe after another. He's struggled with the reality that being a successful mayor of NY means doing a lot of little, unsexy things -- kissing asses of interests you don't particularly care about, getting the snow plows out, keeping police / fire / sanitation happy with their contracts, keeping businesses from leaving for NJ, keeping the MTA working, finding a way to budget successfully when there isn't enough money. He doesn't seem to like the actual job. About all he's accomplished is being the protestor-in-chief. Which is a great job. It's just not what MOST people really want of the mayor.