flat on one's ass
1. Fig. Inf. completely exhausted. (Potentially offensive. Use only with discretion.) I'm just flat on my ass. I need some rest. After the day of the marathon, Pete was flat on his ass for a week.
2. Fig. Inf. broke; financially destroyed. (Potentially offensive. Use only with discretion. An elaboration of flat broke.) Sorry, I can't help you. I'm broke—flat on my ass. The guy's flat on his ass. Can you help him out with a loan?