“He’s a terribly good chap, but he always forgets to pass the port.”
Port etiquette is a little strange but also very helpful. Its considered bad form to fail to pass a port decanter whilst there is still some in it. Being British though, we can’t simply point this out, so instead the tradition is to ask the person in possession of the decanter if they know the Bishop of Norwich.
If they are familiar with this tradition they’ll apologise and pass it, otherwise you’ll have to politely explain using the quoted sentence above.
This oddity aside port etiquette is pretty practical and highly sociable. The tradition is that the decanter is passed to the left with the person receiving it pouring a glass for the person on their right before passing it on. Any pauses can be remedied with by an enquiry about the good Bishop.
Nobody knows why the Bishop of Norwich bares the historical brunt of this tradition, nor which Bishop it actually refers to. Similarly, nobody knows why port goes to the left. Perhaps using your left hand allows you to keep your sword hand ready to defend yourself against anyone who is about to impune your honour. Maybe its because Port is synonymous with the Navy and the port side of a boat is on the left when facing the bows (front).
Never-the-less the reason the decanter has to keep moving is because its highly likely the contents are a vintage port. Vintage ports start to lose their character and their quality as soon as they are opened, so you’d be wise to drink up and pass the decanter as quick as you can.
Image is of Richard Corbet, Bishop of Norwich 1632 – 1635, by Sylvester Harding (British Museum) [Public domain], via Wikimedia Commons