"Cool boss" or not you can't legally do free work under an employer. OP has to get paid, they just don't get a day off in this case

i wonder what you gain from being an asshole for no reason

Do they actually have to pay him? It's kind of a weird case, true a lot of this depends on what kind of job / work OP does. It's a weird scenario because OP's boss did not ask OP to come in nor authorize possible overtime (depending on how many hours OP has already worked that pay period). So is this something a business has to cover (anytime an employee decides to show up and work regardless of a schedule) or did OP indeed put in some free hours. It would be nice for OP to get compensation but regardless it's a lesson learned. Honestly don't know the answer.

This would be an interesting legal case to handle. I don't know laws in Victoria (or all of Australia, for that matter), but in Canada there are protections for the employer so employees can't just show up and do work and demand money. Of course the purpose of the law is not to disadvantage people in honest mistakes or miscommunications, so if you want to know the "spirit" of the law, even if the employer isn't legally required to pay OP, I could see OP having a legal case for demanding wages. Of course, this is all hypothetical and based on my assumptions. Just sort of thinking out loud here.

In the US, an employer would always have to pay under Federal law. I'd think any modern country would have similar regulations.

When I used to work for Walmart they was ask(tell them they had to) people to work "volunteer" time and vaguely imply that if they didn't they would get the shifts no one wanted because they weren't a "team" player that was if they would schedule them at all for two weeks

Walmart isn't a great example to use because they're terrible employers. And a pretty terrible company in general. That situation is different because they actually get the employee's consent to work sometimes for free. Thus the employee has no case to get paid for those hours.

It is against Walmart company policy to work off the clock. Not only is it bolded in the employee handbook it was posted throughout employee areas. Also depending on what job you do, you wouldn't be able to perform your job as you need to be clocked in to use any electronic equipment.

yeah but it was their day off regardless, I worship all of my time off