What's the worst friendship fallout you experienced?

My best friend of 10+ years stabbed me in the back by having 3 of her friends (complete strangers to me) move into our shared apartment while I was away on vacation. Then when I returned, the apt was trashed, and they had 2 dogs living there too, and they didn't clean up after them so it smelled like piss in there. I told her she would have to make her friends move out. She refused. So I moved out and never talked to her again.