He's an idiotic fool.
Ignore his bluff, and unplug your router to change your IP, or just fuck with him and use reverse psychology on him.
I've been threatened to be DDOSED before when logging into a Ventrilo by some kids before.
I told them I guessed there Admins password (which was a 16 year old kid), they didn't believe me. I logged onto the Admin account > Rcon > Typed command "Status", afterwards put there IP's into the comment box for proof, instant respect afterwards. Course, I perm banned them from that Ventrilo just for being idiotic fools, couldn't let a opportunity like that pass by. : P
~ DD