Greece was the 16th stop in his two-year-long round-the-world trip and he'd often been warned about people dressing in fake uniforms to extract money from backpackers, so while he handed over his passport he also asked the man to show him his police ID.
Instead, Jung says, he received a punch in the face.
Within seconds, the uniformed man and his plainclothes partner - the man who had first approached Jung - had him down on the ground and were kicking him, according to the Korean.
In shock, Jung was by now convinced he was being mugged by criminals and began shouting for help from passers-by.
"I was very scared," he says.
It was only when he was handcuffed and dragged 500m (500 yards) up the road to the nearest police station that he realised he was actually under arrest.
Jung says that outside the station the uniformed officer, without any kind of warning, turned on him again, hitting him in the face.
When Jung was released from police custody without charge just a few hours after being detained, he says one officer shouted after him, "Hey Korean, go home!"
When police stopped him in central Athens he showed them his US passport, but they handcuffed him anyway and took him to the central police station.
They gave no reason for holding him, but after a few hours in custody Ukwuorji says he was so badly beaten that he passed out. He woke up in hospital.
"I went there to spend my money but they stopped me just because of my colour," he says. "They are racist."
It is impossible to determine how many people have had a similar experience - but enough Americans for the US State Department to issue a warning to its citizens travelling to the country.
It updated its website on 15 November to warn of "confirmed reports of US African-American citizens detained by police conducting sweeps for illegal immigrants in Athens", as well as a wider problem in Greek cities of "unprovoked harassment and violent attacks against persons who, because of their complexion, are perceived to be foreign migrants".
Tourism is a major source of revenue in Greece, especially important at a time when many other businesses are going bust. Anything that deterred visitors in large numbers would be a disaster for the economy.
Lt Col Christos Manouras of the Hellenic police force says operation Xenios Zeus, launched last August, has slowed down the flow of illegal immigrants. Anyone who looks foreign, or who has aroused suspicion, may be stopped, he says.
"If someone is stopped by the police and they do not have a valid means of identification we will accompany them to the station until their nationality can be determined," he explains.
"I think that is normal and I would expect Greeks to be subjected to the same treatment abroad."
But while more than 60,000 people have been detained on the streets of Athens since it was launched in August 2012, there have been fewer than 4,200 arrests.
And some visitors to Greece have been detained despite having shown police their passports.
you think they'll be gladly to have the tourist dollars etc.. but instead they beat up none white tourist. white tourist from europe and america aren't the only tourist now days.
I like to stick it to The Man, The Man happens to be Liberal in NYC(power Structure).