For the "bill" itself, we can't see the other side, but there's enough differences that you wouldn't mistake it for real currency at more than a glance. Fake bills for movie/tv sets look far closer to real bills (basically with obviously fake serial numbers and "for movie use only" stamped on it.

For leaving it as a tip, it's not being used to satisfy a payment. While tipping is expected, it's not required and there's not an agreed upon amount between the parties. So they're just leaving a scummy flyer behind. Not any different than the people that 'tip' with Chick Tracts. If they were to use it to try and pay the bill, it'd be illegal.

It is clearly marked as not being a $20 bill. That 2024 is huge compared to the real thing. The flip side probably includes a picture of Donnie T instead of Jackson.

If you accept that as legal tender, it's on you. On the bright side, there's no indication that they were trying to pass it off as real money. It's like those screeds where it looks like a $20, but you open it and it says, "I bet you would have been happy if this was real money, but let me tell you, Jesus is better than money."

Gee, thanks. Let me ask the HEB of they'll accept Jesus in exchange for milk and beef.