I was a good roommate except for that one time...
What happened that one time?
I ate all my roommates food.
If it was only one time, then there's nothing to be concerned about. You can just pay them back.
Heck no, it's in the past and I don't really care about them.
You are more than welcome to decide on your own, but since you didn't make amends, I guess you will always have something that you had done that you are not proud of.