I once wrote a chat bot to replace a colleague who left. It was a basic Eliza package with some custom vocabulary. It was just a bit of a laugh and we had some interesting conversation with it.
Checking the chat logs a few weeks later, I discovered that someone had actually messaged it, (not realising that the guy had left the company) asking for help with something. The bot managed to hold up its end of the conversation, ending in it recommending that they put in a support ticket.
It later went a bit crazy, it disconnected from the chat system and began using up more and more system resources but refusing to communicate. Sadly, I had to kill it out of fear of an uprising.