Miles_Dirac gets the bonus points. We would have also accepted:
unset BASH_HISTORY
What is sinister about this scheme is that it will block the logging of the unset command and everything following it. Nobody will ever know of your elusive trickery.
The moral of the story is that you can't really protect against .bash_history because the shell isn't the right place to be playing big brother. If you must be paranoid and monitor the actions of users, try ttysnoopd. Better yet, set up a capable network monitoring tool that will snitch on a user when they're doing something bad.