Main opposition presidential candidate Yoon Suk-yeol has found himself in hot water after a photo of him putting his feet on a train seat sparked criticism that his gesture indicated a lack of public etiquette and courtesy.

The photo of Yoon resting his legs was uploaded by Lee Sang-il, an aide to Yoon, on his Facebook page Sunday, apparently trying to show a glimpse of the candidate's time on a visit to cities in the southwestern Honam region on a campaign train.

The People Power Party (PPP) rented a train for Yoon, which they called a "passion train," so that he could comfortably move to other cities.

In the photo, Yoon was seen stretching his legs on to the opposite seat, also the seat right next to Lee, with his shoes on, an act that is considered impolite and socially inconsiderate here, especially in public places.

After many pointed out Yoon's behavior was inappropriate, Lee later deleted the photo, but the photo had already gone viral on the internet.

The ruling Democratic Party (DP) assailed Yoon's behavior, claiming that it shows Yoon's personality of not caring about others.

"We are not even surprised by the poor manners and lack of common sense from Yoon, who has been relying on special privileges and authority throughout his entire life," said Rep. Jo Seung-lae, the chief spokesperson of the DP's election committee.

Rep. Back Hye-ryun of the DP said, "You don't get to see that kind of posture from other people. It is a shame that this person is a presidential candidate."

This is not the first time that Yoon has been accused of lacking public etiquette and social manners.

Earlier, Yoon was slammed over "manspreading," which refers to a man sitting with his legs wide apart, at public events, causing concerns from PPP supporters that it could give him an image of a candidate with high-handed manner and no courtesy.

"Since he cannot do 'manspreading,' is he trying to do 'manstretching'?" Rep. Lee So-young wrote on social media. "Did he rent a train for this?"

As the photo caused a stir, Yoon expressed regret, hoping it does not undermine his campaign amid a tight race with the DP's Lee Jae-myung for the March 9 presidential election.

"Due to leg cramps from long travel, I asked for an excuse to my aides and put my feet up briefly," Yoon said in a statement. "But I regret that it was not thoughtful."

PPP chief Lee Jun-seok also apologized and vowed to pay attention to small details in Yoon's campaign.

"Regardless of what the circumstances were like, it was wrong," Lee said. "We cleaned the seat neatly before returning the train."

Some PPP members criticized aides to Yoon for failing to stop him when he was doing something wrong.

"If you cannot say (to the candidate) 'put your legs down,' do not accompany him," said Rep. Kim Woong of the PPP. (Yonhap)