If memory serves correctly, once a user could click on the little upper button and leave a chatroom. That button is shown below:
But recently, I started noticing that this is no longer the case – once you click the button, you check out of the room for a period of time, then Stack Overflow automatically logs you back in after a while.
I understand how chat bugs are as important to SE development team as a neighbourhood stray cat to a dog loving family. But I feel morally obligated to report this, just like I would feel guilty for not telling you there is a hole in your backyard after someone fell into it when we came for a BBQ gathering.