Immoral? Depends on the moral system, but in not aware of any that would directly support fucking over individuals. Tips, handouts, that's shitty by any moral system I've ever run across.

Unethical? Well, ethics are situational. But, again, I can't imagine any code of ethics that would say fucking over an individual would be okay.

Illegal? Ask someone else. I'm fairly sure there's places where it would be illegal to pass fake money at all, but im damned if I'll go looking it up for you lol. I do know that passing counterfeit bills is illegal anywhere that bills are used, the only question would be if fake money that isn't an attempt to mimic a real bill would count.

Now, the leeway you have on moral and ethical realms is in church donations. They have to count and process the cash before it can be used, so the chances of it fucking a person over approach zero at the least. And if it's deposited in a bank, it'll get caught, and likely not result in harm to anyone involved. So you could make an argument that, it isn't immoral, just really cowardly behavior if you have a choice of donating or not. Social pressure is not enough to excuse just being a fucking adult and not putting it on the plate.

If you don't have a choice, as in it would bring harm beyond just not being welcomed back to that church, then it isn't a voluntary donation, which gives you the moral and ethical freedom to take whatever steps you need to survive until you can leave the situation that has you there.

As much as I hate tip culture, leaving a fake tip is just a giant, gaping asshole move. Fuck anyone that does that. Be a fucking adult and just don't tip, or find establishments that tipping isn't a factor.

Also, having bounced at strip clubs, you should be aware that trying that shit at any decent club is going to cost you way more than money if you get caught. I was a fairly gentle dude, and I would have literally bounced your ass off the pavement if I could lift you. Any bouncer I ever worked with would have too. Baaad idea to fuck around at places that tend to be no go zones with cops, especially if you don't know for a fact that it isn't laundering money. If it is a laundering front? You are going to get hurt, bad. Those kind of places are not friendly to fuckery like that. Say whatever you will about strippers, but they work a shitty job for shit money, dealing with creeps and assholes the entire time (not always the customers tbh). That tip may actually be all they get paid in some places.

I assume you're asking hypothetically, so please don't take any of that as a direct comment on you as a person. The response is to the hypothetical person, if you get what I'm saying. Nothing wrong with asking the question.