RIO DE JANEIRO — As millions of Brazilians enjoyed the last few hours of Carnival, Jair Bolsonaro, Brazil’s far-right president, denounced what he said was the debauchery of the festivities, and posted a video on Twitter that he presented as graphic proof.

“I don’t feel comfortable showing this, but we have to expose the truth so the people can be aware,” the president wrote alongside a video he posted that showed one man urinating on another in public. “This is what many street parties during Carnival have turned into.”

The video shows a man, wearing a black jockstrap, dancing on what appears to be a bus stop. At one point a second man urinates on the head of the man in the jockstrap. Mr. Bolsonaro urged his 3.4 million Twitter followers to draw their own conclusions and comment on the video.

Although Mr. Bolsonaro said the video represented a kind of behavior that is increasingly common during Carnival — a cherished, if hedonistic and boozy, cultural institution in Brazil — the reactions of Brazilians who disagreed poured in.