How To Delete a User Account? - MySQL FAQs - Managing User Accounts and Access Privileges

If you want to delete a user account, you can connect to the server as "root" and use the "DROP USER ..." command to delete a user account. The tutorial exercise below shows you a good example:

>cd \mysql\bin
>mysql -u root -pretneciyf mysql

mysql> SELECT User, Password, Shutdown_priv FROM user;
+------+-------------------------------------------+-----+
| User | Password                                  | ... |
+------+-------------------------------------------+-----+
| root | *3735F1D8464342BA852E10101E55E422EBAAAF35 | Y   |
| dev  | *446BD97F308FBA0B9CBDC962C2842AD338BCE59E | N   |
+------+-------------------------------------------+-----+
2 rows in set (0.01 sec)

mysql> DROP USER dev;
Query OK, 0 rows affected (0.63 sec)

mysql> SELECT User, Password, Shutdown_priv FROM user;
+------+-------------------------------------------+-----+
| User | Password                                  | ... |
+------+-------------------------------------------+-----+
| root | *3735F1D8464342BA852E10101E55E422EBAAAF35 | Y   |
+------+-------------------------------------------+-----+
1 row in set (0.01 sec)