Syntax:
REVOKE
    priv_type [(column_list)]
      [, priv_type [(column_list)]] ...
    ON [object_type] priv_level
    FROM user [, user] ...

REVOKE ALL PRIVILEGES, GRANT OPTION
    FROM user [, user] ...

The REVOKE statement enables system administrators to revoke privileges
from MySQL accounts. Each account is named using the same format as for
the GRANT statement; for example, 'jeffrey'@'localhost'. If you specify
only the user name part of the account name, a host name part of '%' is
used. For details on the levels at which privileges exist, the
allowable priv_type and priv_level values, and the syntax for
specifying users and passwords, see [HELP GRANT]

To use the first REVOKE syntax, you must have the GRANT OPTION
privilege, and you must have the privileges that you are revoking.

To revoke all privileges, use the second syntax, which drops all
global, database, table, column, and routine privileges for the named
user or users:

REVOKE ALL PRIVILEGES, GRANT OPTION FROM user [, user] ...

To use this REVOKE syntax, you must have the global CREATE USER
privilege or the UPDATE privilege for the mysql database.

URL: http://dev.mysql.com/doc/refman/5.1/en/revoke.html

