I'm a cashier and whenever I have a rude or customer or one with an attitude I give them the dark oxidized pennies in their change while new moms and nice customers get the new shiny pennies.
Is there something that you are trying to prove by doing that?
It's a form of revenge for me, I have mommy-issues.
I do not think that it is okay to take things like that out on customers. You should treat all your customers with respect and courtesy, even if they don't do the same for you.
I'm mad at their moms and dad for not giving them a good life.
That sounds like a good point, maybe these customers are disrespectful to you because they weren't raised properly or taught the right ways to behave.  However, that means that you shouldn't be taking out your frustrations on them, even in harmless ways like this.  Just try to set a better example, and maybe they'll learn.