If I'm in a room with people I know and I plan to leave the room for a long time, I tell them where I'm going. If it's for a short time I do not.
What (if anything) is an appropriate time scale to leave a room without announcing when/if you'll be back?
in social circles with unknown people (a bar for example), it is common curtesey to stand up, raise a glass and shout in full volume "I'm going to the shitter, yo!" before doing exactly that
I like to avoid a social faux pas in this situation and just shit my pants.