How do you feel about me not giving my classmate $20?
Do you have a $5 bill? Maybe you can afford that much?
She's done nothing for me. I'm not going to give someone $20 for no reason.
Then you can make the first move, it is just a favor out of the kindness of your heart. Maybe one day she will return the favor after your generosity.
I'm not feeling like it.
Well, if you don't feel like it then keep the money for yourself. You won't feel better about yourself but you will have that $20 to spend on anything you like. Its your money to decide either way.