A dollar bill or any other money is dirty.
A dollar bill is dirtier in reality than a toilet seat.
When you touch a dollar bill or any other money you can easily get germs, viruses etc from the money if you do not wash your hands properly after touching it.
If you think about it a dollar bill or other money has been circulated around a lot and thousands of people have likely touched that dollar bill that you're now touching.
Some people put the dollar bills down their pants, in their panties, shoes, in their bras etc.
The person could've masturbated etc and then touched the money.
So money is really dirty and has more germs really than a toilet seat but most people never really think about that.