Sad.

Mayor Bill de Blasio’s 2020 presidential-bid YouTube page had just 61 subscribers nearly 10 hours after he posted his big campaign announcement there — and his flat-footed social media effort has drawn fire from Donald Trump Jr.

While some 24,313 people have viewed his campaign page created on May 15, just 59 were enticed enough as of 3:30 p.m. Thursday to subscribe to the page — meaning they’d get updates when he posts new videos, according to his YouTube page.

“this guy is the mayor of a city of millions but only has 51 followers thats pretty much the same amount of votes hed get,” one user posted on the account’s discussion page around 3 p.m.

A tweet sharing de Blasio’s campaign announcement video fell similarly flat.

The message got 4,100 replies and just 208 retweets by 3:30 p.m.

Conventional web wisdom states that a high ratio of comments to replies means a tweet was a flop — because retweets spread your message while comments are typically negative.

“I’m just here for the ratio,” tweeted Donald Trump Jr., who is no stranger to getting ratio’ed, in response to the de Blasio campaign tweet.

By 3 p.m. Thursday, de Blasio’s announcement video — over which he is already taking heat for filming inside Gracie Mansion — had been viewed about 31,000 times in the four hours it had been live, YouTube stats show.