Don't save current bash session to history
Solution 1:
Unset the $HISTFILE variable
$ unset HISTFILE
If HISTFILE is unset, or if the history file is unwritable, the history is not saved.
http://www.faqs.org/docs/bashman/bashref_106.html
Solution 2:
Perhaps more elegant than crashing bash would be to use the history -c command to clear the history of the current session. Then, there's nothing to save (it even wipes itself from the history).