A magistrate described Nabel Quzag's conduct as obnoxious, reprehensible and worthy of condemnation.

But Bernadette Boss said handing over false identification and giving a false name to police who already knew who he was did not amount to hindering.

The 20-year-old man pleaded not guilty in the ACT Magistrates Court to a charge of hindering a public official in the exercise of their duties.

The prosecution alleged Quzag handed over his brother's ID, and used his brother's name, making it ''substantially more difficult'' for the officer in question to do his job.

An off-duty police officer spotted Quzag eating with two other men, including Moustafa Negro, at the Grilled burger joint in Belconnen in January. Negro was on bail for a string of alleged offences at the time, with conditions banning him from being in Quzag's company. The off-duty officer reported the interaction and four on-duty police arrived at the restaurant to arrest Negro.

When one asked which one of the group was Quzag the defendant said ''He's not here''. Quzag gave his brother's name and ID, but when pressed became aggressive.

His lawyer, Michael Kukulies-Smith, said his client's conduct on the day ''may have, to use the vernacular, failed the dickhead test''.

But the defence argued the offence of hindering police was not proved because the officers already knew who he was.

Dr Boss found the charge not proved.

''Undoubtedly the defendant was rude, obnoxious, his conduct was reprehensible and worthy of condemnation through his behaviour and the words used,'' Dr Boss said.

She rejected the defence's application for costs, saying Quzag brought the hearing on himself because of his behaviour.

Quzag pleaded guilty to a charge of possessing a licence issued to another, has also breached a good-behaviour and has admitted an unrelated breach of bail. He is due to be sentenced on those matters in October.