I'll forge a rubber check for you
What you yell at someone who whines about getting paid for something you already gave them for free. It’s like saying you’re gonna write them a fake check with fake ink, double nonsense.
You: 'I’ll forge a rubber check for you!' (after your buddy asked for cash for a sandwich you threw away.)
You: 'I’ll forge a rubber check for you!' (because your cousin wants money for a toy you already gave him.)
You: 'I’ll forge a rubber check for you!' (after your friend asked for a $20 tip for a pizza you already ate.)