Oops, I created a SQL user with an upper case letter.
createuser --interactive $ myUser
then I tried to create a corresponding Unix user:
sudo adduser myUser -> bad name
OK, create an all lowercase name:
sudo adduser myuser
Now create that user in SQL:
createuser --interactive $ myuser
\du -> myUser -> myuser -> postgres
Huh, so we want to delete the first user:
DROP ROLE myUser; -> cannot drop current user
This is because SQL folds unquoted names to all lowercase, so the command that SQL is actually interpreting is
DROP ROLE myuser;.
To actually remove the myUser role:
DROP ROLE "myUser"; -> DROP ROLE