I'm mad at my girlfriend when she wants me to pay back the money she spent on me
Why is she making you pay that money?
Because I don't have that money and I don't like her gift.
When someone chooses to give you a gift, it is expected that the receiver will not have to pay them for the gift. You should return the lamp to your girlfriend instead.
I want a lamp that says "MOAR BOOZE".
Grow up and be professional.