Why was Darry upset with Ponyboy for falling asleep in the lot?

Darry was angry because Ponyboy came in long after curfew, and he was worried about him.

"Where the heck have you been? Do you know what time it is?" He was madder than I'd seen him in a long time. I shook my head wordlessly.
"Well, it's two in the morning, kiddo. Another hour and I would have had the police out after you. Where were you, Ponyboy?"--- his voice was rising--- "Where in the almighty universe were you?"