To Flávio Bolsonaro and his publicists, it must have seemed an ingenious idea that would expose his rival’s supposed crookedness on the eve of Brazil’s presidential election.

But the far-right politician’s decision to attend a primetime television debate against his leftwing opponent, Luiz Inácio Lula da Silva, with the word “corrupto” (corrupt) written on the palm of his hand has backfired.

Rather than drawing attention to the incumbent’s alleged misdeeds, many of the programme’s millions of viewers sarcastically took Bolsonaro’s hand-written message as an admission of his own guilt.

Following Sunday night’s debate, Lula supporters from all walks of life have flooded social media with photographs of their own self-descriptions inked on their palms.

John Ulhoa, the guitarist from a pop rock band called Pato Fu, jokingly described himself as a “musician (and a hunk)”.

The Emmy-winning comedian Antonio Tabet introduced himself to his 2.8 million followers on X as an artist.

Carlos Marcio used both palms to portray himself as a cellist and author.

Carla Emanuela Sacramento, an obstetric nurse, posted a photograph of herself clad in personal protective equipment and with the words “primary health care nurse” proudly written on her right palm.

Prominent politicians also jumped on the trend, including Lula’s health minister, the infectious disease specialist Alexandre Padilha, whose palm noted he was a doctor, and Tabata Amaral, who identified as a political scientist and astrophysicist.

All across the country, librarians, oil workers, engineers, journalists, architects, pilots, psychologists, seamstresses, street cleaners, teachers, influencers, and police officers used ballpoint pens to inscribe their professions on to their skin.

Writing on Substack, the Latin America expert James Bosworth called Bolsonaro’s stunt a “critical error” in his bid for power.

“It may have seemed like an inspired pre-debate gimmick. Instead, he gave the world a meme image that will stick with him for the rest of his political career,” Bosworth said, offering politicians a word of advice.

“Don’t write the word ‘corrupto’ on your hand and show it to the audience,” Bosworth suggested.

Bolsonaro, who is the son of the jailed former president Jair Bolsonaro, is a professional politician who has long faced corruption accusations, although he denies them and has never been convicted. The 45-year-old senator also has well-documented ties to members of Rio’s mafia underworld and once employed the relatives of the city’s most notorious contract killer, Adriano da Nóbrega. Last week two allies were arrested for alleged involvement with the Red Command drug faction, which Donald Trump recently designated a foreign terrorist organisation. Bolsonaro voiced surprise at those arrests and said the men had the right to prove their innocence.

On Monday, Brazilian media reported that Bolsonaro was being investigated by the federal police as part of a money-laundering inquiry.

Lula, whose Worker’s party (PT) has also been involved in major corruption scandals, used Sunday’s debate to throw down the gauntlet to Bolsonaro.

The leftwing incumbent said he would give electoral authorities access to his banking and phone recordings, and those of close relatives, in order to prove he was not corrupt – if Bolsonaro agreed to do the same.

Bolsonaro, who, polls suggest, holds a slender advantage ahead of Sunday’s second-round runoff, has yet to respond to Lula’s challenge. The rightwinger won the 4 October first round by more than 2m votes.