Democratic socialist and self-described “nepo baby” Zohran Mamdani fronted the first general-election mayoral debate desperately wanting voters “to see him as tough” as he threw punches at his “bedraggled” rival, ex-Gov. Andrew Cuomo, a body language expert told The Post.

“Mamdani was, ironically or purposefully, dressed in black like a villain,” brain and body language expert and psychiatrist Carole Lieberman said in the wake of Thursday night’s showdown.

“He was either showing his true colors unconsciously or wanted viewers to see him as tough.”

The 33-year-old upstart — whose mom is an Academy Award- and Golden Globe-nominated filmmaker and whose dad is an author and chaired professor at Columbia University — has even joked that he has benefited from nepotism.

He has also come under scrutiny for his short resume and lack of experience in local government.

Lieberman said the mayoral front-runner was smug, too, as he jostled with Cuomo, who is running as an independent, and Republican nominee Curtis Sliwa, ahead of next month’s election.

“He also perpetually wore a cat-that-ate-the-canary, smug smile, as if he was already thinking about how he would decorate the mayor’s mansion,” the expert said — though she noted the socialist upstart seemed “a little more nervous” than usual.

“He seemed angry, as if annoyed that he still had to debate to prove he’s the best candidate. His tense anger was made visible by his clenched jaw, erratic hand gestures and squinting,” Lieberman said.

Cuomo, on the other hand, looked worse for wear.

“[He] looks bedraggled. He could pass for a homeless person on a Central Park bench,” Lieberman noted, adding that the stress of the campaign was taking a visible toll.

“He looks almost sickly,” she added.

By the end of the debate, the former governor “looked worried” like “he feared he hadn’t gotten enough of an edge over Mamdani,” the expert said.

In direct contrast, Sliwa — who was without his iconic red beret — was the “most relaxed and friendly” of all three candidates.

“His wide arms, on either side of the podium, indicated that he was also the most open,” Lieberman noted.

“He was a welcome island of calm, a respite for viewers from Cuomo and Mamdani, who made viewers nervous.

“His clothing mirrored his calmer attitude,” she added.

A Fox News poll released just before the debate started showed Mamdani breaking 50% for the first time in the contentious race so far.

The Democratic socialist garnered 52% of likely voters, with Cuomo and Sliwa trailing at 28% and 14%, respectively, the poll showed.