Revoking Privileges on all objects

Yet another SQL-generating-SQL candidate:
I have no means to test it, as my databases don't have a lot of roles, users and grantees - but I think I can get the syntax right...

SELECT
  'REVOKE '
||CASE object_type WHEN 'ROLE' THEN '' ELSE 'ALL ON ' END
||CASE WHEN object_schema IS NULL THEN '' ELSE object_schema||'.' END
||object_name
||' FROM '||grantee||';'
FROM v_catalog.grants WHERE  grantee IN ('scott','tiger','fred','allofthem')
;

The report of this will be the script you'll have to run. Should work - at least after a few tweaks...

I've tried something similar to Marco idea for user Mike and it works:

\a
\t
\o | vsql
SELECT
  distinct 'REVOKE ALL ON ALL TABLES IN SCHEMA ' || object_schema || ' FROM ' || grantee || ';'
FROM v_catalog.grants WHERE grantee='mike' AND object_schema != 'NULL';

You may want to add also the following because tables owners can still access their own tables:

SELECT DISTINCT 'alter table ' || table_schema || '.' || table_name || ' owner to dbadmin;'
FROM tables WHERE owner_name = 'mike';