You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
With unwell American Katie Ledecky sitting out the 200 freestyle heats in the morning, and later confirming she would skip her 1500 title defence, Tuesday's calm early session gave no indication of the fireworks to come.
Sun, who is swimming under a cloud in Gwangju with the Court of Arbitration for Sport (CAS) set to hear a doping case against him in September, came home second in the 200 but got the win when Lithuanian Danas Rapsys was disqualified for a false start.
At the medal ceremony, Scott shook hands with fellow bronze medallist Martin Malyutin, of Russia, who finished with the same time as the Briton, but then completely cold-shouldered Sun, refusing to make eye contact and not offering a handshake.
Sun was livid, yelling and gesturing at the 22-year-old Scott, and later confronting him as the medallists walked off the podium towards the stairs leading to the pool deck.
"You loser, I'm winning, yes," he spat at the Glasgow-born Scott, who ignored the taunt and kept walking with his hands behind his back.
The incident comes after Australian Mack Horton refused to share the podium with Sun after the Chinese swimmer won the 400 freestyle on Sunday.
Sun, who served a doping ban in 2014 and was labelled a "drug cheat" by Horton before the Rio Olympics final, got the green light to compete in Gwangju after being cleared by a FINA panel of breaching the governing body's rules earlier this year.
However, the World Anti-Doping Agency is seeking to overturn the decision at CAS, leaving Sun's career hanging in the balance a year out from the Tokyo Olympics.
American Lilly King has never shied away from voicing her opinions about doping in sport, particularly concerning her rival Yuliya Efimova, but after winning the 100 breaststroke on Tuesday there was little sign of any animosity between the two.
King accepted a handshake in the pool from the Russian, who who served a 16-month doping ban in 2013, and they embraced on the podium - a far cry from the tense news conferences of Rio 2016 after the American had called her rival a drug cheat.
"I wouldn't say we have completely moved on but we are definitely more cordial than we have been," King said of Efimova, who took silver.
"I think it was kind of blown out of proportion a little bit, the whole situation, but again we've both grown up since then."
Ledecky's absence from the 1500 final, which she won at the last three worlds, opened the door for Simona Quadarella, the Italian taking gold in 15:40.89 - more than nine seconds outside the American's winning time two years ago.
"When I knew Ledecky wouldn't swim in the 1,500 I didn't know if it was a good thing or a bad thing," said Quadarella, who added that claiming gold was "a dream".
Ledecky had been gunning for four individual golds at the worlds but saw her run of three straight 400 titles ended by Australian Ariarne Titmus on Sunday.
While there was no news on whether the 22-year-old will defend her 800 crown, the American may leave these championships without adding to her haul of 14 world titles.
Both 100 backstroke defending champions retained their titles with Canadian Kylie Masse (58.60) winning the women's race and China's Xu Jiayu the men's (52.43).
Britain's Adam Peaty, who won the 100 breaststroke gold on Monday, was fastest in the semi-finals of the 50 and will look to complete a third straight 50/100 double on Wednesday.