You can boot into single-user mode and wreak all the havoc you want, assuming you know your way around a UNIX terminal. If not, there are plenty of tutorials available with super-simple Google searches. It is beyond the scope of this forum to teach someone the UNIX command line (it would be like asking someone to teach you the encyclopedia), but help is out there ready for you.
You cannot delete the user account you are currently logged in from -- there is no hack or whatever. It is simply impossible. You can do a lot of damage (deleting files, etc.) such that after a log out, you wouldn't be able to log in again with that user account, but the user account would still exist in the system. You can only delete a user account while logged in as another user -- for one, this prevents you from deleting the last user account on the system, which would be terrible if you ever wanted to use the machine.