I ate my coworker's lunch when I was in the breakroom.
Why would you eat your coworker's lunch?
I was hungry and I didn't have my own lunch, I didn't think he would mind.
It's wrong to eat a lunch that doesn't belong to you. If you want to have lunch, you need to bring it or buy one. Eating someone's lunch without asking is unethical and very rude.
I don't think it's that big of a deal. I mean he walked away from his lunch. What was I supposed to do?
You should just leave his lunch alone in the future. How would you feel if you came back from the restroom and your lunch was gone?