Use visudo to edit /etc/sudoers.

Specifies that root can run anything anywhere:

root    ALL=(ALL) ALL

User nobody can run sshdkill as root without entering a password:

nobody  ALL=NOPASSWD: /usr/local/bin/sshdkill

Insults

Add "insults" to your Defaults line then type an incorrect password.

Defaults        !lecture,tty_tickets,!fqdn,insults

That's funny but sudo is still a mess.