Sit him down, remind him that you aren't and weren't in the military so stop trying to push that on you. You're not signing up for boot camp anyway. Also let him know you had no issues until he arrived and made issues which is now hurting the company, and BCC your previous boss on an email about it if needed. Hell, go ask to chat with the boss and see if he can help if it's that bad.
Either that or dude was hired to go all REPO on your ass and run you off. And since he WAS military, the term "eat a bag of dicks, you hot racking squid" is an acceptable way to tell him he is a piece of shit that's ****ed up like a football bat.