Please tell him to "shut the **** up!" please please please Thing is, he's a big bloke, ex-military, bangs on endlessly about his post-traumatic stress thingy (not belittling this at all, but if you knew him I guarantee you wouldn't be impressed) and I actually think he could be a borderline psycho.
Better simply to avoid rather than confront, probably.
Only in times of extreme danger and very real threat of getting filled in must you use the following tactic...
kick him in the nuts and run!