Forgotten Food
If your first reaction after looking at this picture was “Ugh, that’s disgusting,” we don’t blame you. A dirty sink is one thing but this is absolutely unacceptable! The OP was away for a few days and came home to find that their roomie had conveniently “forgotten” some food on the kitchen countertop.

They even left the crockpot unwashed and as a result, there was mold growing everywhere. Now, things like this don’t happen overnight. It was clearly left there for quite some time. Not only is that downright gross but it’s also really unhealthy. We hope the OP gave them a piece of their mind.