This has cropped up a couple of times in ~chat-feedback now where the ‘Leave Chat’ button is too hidden to find easily. One of the suggestions is to add it next to where you would find the ‘Join’ button, as well as adding a cross to the sidebar like Personal Chats:
If you click on the channel title, and then flip to the About tab, you should see the option to Leave in there 
For Personal Chat you can press the x icon next to the chat title, but this is currently only available on desktop
One thought I’ve had recently that’d improve this a little bit is to make the About page the first place you go when you click on a channel name, rather than the members list.
We already have an X for personal chats, so that seems like an easy extension for channels
Replicate the Leave Chat button between the About and Settings tab, because the Settings tab is what you get when you click the only remaining visible “more options” button on a joined channel.
After reading this topic and clicking on the pencil button I realize there are more channels to join 
maybe we should make joining more discoverable as well
Curious what we do for groups? It is possible to make groups one can freely join and leave, is there UX we can copy from there?
It would also be very handy as an admin to be able to remove people from a channel. I’ve had a couple of times when I’ve accidentally added a whole bunch due to a rogue group added to the category security settings and the only way to deal with it is to delete the channel.
If we’re not talking hundreds it’s also an option to impersonate and leave on their behalf.
That is a pain for more than one or two!! And you can’t impersonate Admins (the ones I most frequently accidentally include).
