I found about USER table in an application originally developed against MySQL that has since had Oracle support added.

Along the same lines:

CREATE TABLE T1(
  "USER" VARCHAR2(30),
  C2 VARCHAR2(30) DEFAULT USER);
. 
SELECT
  USER
FROM
  T1;
. 
no rows selected
. 
INSERT INTO T1("USER") VALUES ('HOOPER');
. 
SELECT
  USER
FROM
  T1;
. 
USER
------------------------------
TESTUSER
. 
SELECT
  USER,
  "USER"
FROM
  T1;
. 
USER                           USER
------------------------------ ------------------------------
TESTUSER                       HOOPER

Now, let’s create our own USER function to see if we can make things worse:

CREATE OR REPLACE FUNCTION "USER" RETURN VARCHAR2 IS 
  BEGIN
    RETURN 'CHARLES';
  END "USER";
/
.  
Function created.
. 
COLUMN USER FORMAT A15
. 
SELECT
  USER,
  "USER"
FROM
  T1;
. 
USER            USER
--------------- ---------------
TESTUSER        HOOPER
. 
SELECT
  TESTUSER."USER",
  "USER",
  USER
FROM
  T1;
. 
USER            USER            USER
--------------- --------------- ---------------
CHARLES         HOOPER          TESTUSER

Now introduce a public synonym:

CREATE PUBLIC SYNONYM "USER" FOR TESTUSER."USER";
. 
Synonym created.
. 
SELECT
  USER,
  "USER"
FROM
  T1;
. 
USER            USER
--------------- ---------------
TESTUSER        HOOPER
. 
SELECT
  USER,
  "USER"
FROM
  DUAL;
. 
USER            USER
--------------- ---------------
TESTUSER        CHARLES
. 
DROP PUBLIC SYNONYM "USER";
. 
Synonym dropped.
. 
SELECT
  USER,
  "USER"
FROM
  DUAL;
. 
USER            USER
--------------- ---------------
TESTUSER        CHARLES

Now to clean up the last of the mess:

DROP FUNCTION "USER";
. 
Function dropped.
. 
SELECT
  USER,
  "USER"
FROM
  DUAL;
. 
  *
ERROR at line 3:
ORA-00904: "USER": invalid identifier
. 
DROP TABLE T1 PURGE;
. 
Table dropped.

Precedence (and context)… the same excuse why (1 + 1 * 2) is equal to 3 and not 4.

(Edit:Workpress for some reason is now removing lines with a single space from pre formatted comment sections, so I added a . character at the start of those lines for additional readability).

SQL> select * from user ;
select * from user
*
ERROR at line 1:
ORA-00903: invalid table name

SQL> create table “USER” (n number) ;

Table created.

SQL> insert into “USER” values (1) ;

1 row created.

SQL> select * from user
2 /
select * from user
*
ERROR at line 1:
ORA-00903: invalid table name

SQL> select * from USER ;
select * from USER
*
ERROR at line 1:
ORA-00903: invalid table name

SQL> select * from “USER” ;

N
———-
1