An alleged armed robber with an appetite has targeted a fast food venue in Sydney's south and demanded staff make him a meal during a bizarre hold-up.

Police claim Ryan McGregor, 23, rode his push bike through the drive-through of Hungry Jacks at Engadine about 7pm on Friday and allegedly demanded a meal with what staff initially thought was a pistol.

"Clearly affected by alcohol, [he] doesn't have much recollection of it," lawyer Elias Tabchouri told 9News Sydney.

The incident sent the fast food store into lockdown.

Detectives later seized a piece of cardboard which was wrapped in black duct tape.

"But those who saw it wouldn't have known that and he was seeking food from Hungry Jacks," Tabchouri said.

"In 30 years I haven't seen anything like that."

After he walked through the front door, he allegedly threatened the manager, who made him food, which he ate on a table out the front of the restaurant before police arrived.

Officers arrested McGregor as he enjoyed his meal.

Police claim he had a barbecue cheese burger, onion rings and a coke – an order with a price tag of about $9.

But, it could cost him much more.

If found guilty, McGregor's charge of armed robbery carries a maximum penalty of 25 years in jail.

The court heard McGregor had turned to alcohol since losing his little brother Jarred in a car crash two years ago.

He was refused bail.

"He's very regretful and remorseful, he's actually a good young man," Tabchouri said.