If you want to destroy all Kerberos tickets acquired during your current session, use the kdestroy command. The command destroys you credential cache, which destroys all your credentials and tickets. While this is not usually necessary, running kdestroy reduces the chance of the credential cache being compromised during times that you are not logged in.
To destroy your tickets, use the kdestroy command.
The kdestroy command destroys all your tickets. You cannot use this command to selectively destroy a particular ticket.
If you are going to be away from your system and are concerned about an intruder using your permissions, you should use either kdestroy or a screen saver that locks the screen.