I am a university student and I live with three other people, all students. Overall, we are relatively clean. We have weekly chores that we are all assigned, and the general rule is to wash your dishes within the day you use them. 

On Tuesday, we noticed one housemate (let's call them Housemate A) had not done their dishes in a while. They were starting to pile up and they hadn't been washed out (there was food stuck to them). I had seen an ant in the apartment earlier so I sent a message to the group chat, asking everyone to remember to do their dishes within 1-2 days to avoid bugs. Housemate A responded, saying they could probably not do the stack of dishes until the weekend. They said they were busy since they had 4 midterms, and had no time. I was a little peeved but I told them that I understood they were busy.   
Fast forward to Thursday night, and the dishes were still not done. There was a dead fly in one of the cups, the plates and bowls were not rinsed out, and they were starting to smell. It was so gross. One of the housemates and I started complaining to each other in the kitchen, just saying that we were grossed out, and it was incredibly annoying that Housemate A had left them this long, *especially when we have a dishwasher*. Said nothing bad about them as a person, but we expressed our general annoyance and exasperation with the situation. 

The next morning, we wake up to see that the housemate has posted a long rant on their Snapchat about people they trusted talking behind her back, talking shit, etc. We realized that they probably heard us discussing the dish situation the previous night before. They posted all these quotes about how people are quick to criticize but never congratulate them on their accomplishments -- just generally really passive-aggressive stuff. I feel bad for complaining to my other housemate, but I also don't think they should have left their dishes that long when we have a dishwasher. It's been three days and they have yet to say a word to me or the other housemate; it's pretty obvious they are ignoring us and giving us the cold shoulder. Were we assholes for talking behind their back? I don't want to lose our friendship over this, but I also think they are slightly overreacting. 