They had been drinking hard liquor for five hours at a Korean bar in Tanjong Pagar when he became rowdy and disturbed the other customers.
When the restaurant manager told him to behave, he did not comply and even did something shocking.
Adonas Ho Jue Ting, 27, dropped his pants and exposed his private parts.
Then he grabbed his female companion's face and pulled it towards his groin. He rubbed his groin against her face while doing a humping motion.
The woman, 33, was too drunk to resist but she later told the police that she felt violated and annoyed by Ho's actions.
Ho again ignored the manager's warnings to stop misbehaving and he was later arrested by the police.
He was yesterday jailed a day and also fined $2,000 after pleading guilty to committing an obscene act in public.
Court documents said that Ho and the woman had met for dinner and drank soju, a Korean hard liquor, at WA Bar last December.