Bernie Sanders went ballistic at NBC and MSNBC execs ahead of the Democratic debate this week — jabbing one top TV exec repeatedly in the face with his finger and accusing the networks of offensive negative coverage.

Surging Sanders stormed through the walk-through for the Las Vegas debate, singling out one top producer at the end and aggressively sticking his finger in his face. One shocked witness said, “Bernie marched right up to NBC and MSNBC’s head of creative production and began jabbing his finger right in his face, yelling, ‘Your coverage of my campaign is not fair . . . Your questions tonight are not going to be fair to me.’ ”

Sanders did not hold back as he continued to rant about MSNBC coverage. According to the witness, “The NBC exec told Sanders he would be treated fairly.”

A separate insider confirmed the confrontation, saying Sanders was so steamed he also sparred with MSNBC boss Phil Griffin outside the green room moments before the debate began. “Sen. Sanders stated, ‘Phil, your network has not been playing a fair role in this campaign. I am upset. Is anything going to change? . . . I hope you will do better.’ ”

The Democratic front-runner has been left seeing red over repeated slights against him by liberal MSNBC pundits and hosts, including Chris Matthews, who suggested the senator might cheer socialist executions in Central Park. And Chuck Todd — a moderator of Wednesday’s debate — even quoted a story that described Sanders supporters as a “digital brownshirt brigade.” Todd was also tackled by seething Sanders onstage after the debate: “I do not appreciate your comment about my supporters,” adding the Holocaust reference was “offensive.”

Sanders’ campaign manager Faiz Shakir has said that even Fox News has been “more fair than MSNBC . . . which . . . is constantly undermining the Bernie Sanders campaign.” He told Page Six on Friday, “MSNBC has not been fair to our campaign. Their coverage is condescending on a daily basis. No other campaign gets such negative coverage. Enough is enough.”