I encounter a lot of guys like that, in varying degrees of competent-to-not.

Sometimes I point out that we've learned a lot about handgun shooting since they were in the service (although some of them, I simply cannot believe they were taught to shoot as they do). It's a polite way to start prying off their resistance.

Other times--especially with "empty chamber" or "hammer-down", that sort of thing--I point out that a military handgun is a different animal than a CCW handgun.

In the military, you have a whole host of lethal stuff available. The radio (which calls planes and helicopters and tanks and artillery), grenades, machineguns, rifles, and so on. Basically, a handgun is the second-to-last deadly implement a guy carries, just ahead of a knife. If you need it, the powers-that-be have determined you'll have time to get it ready. They're more concerned with you shooting yourself with it.

In civilian life, the handgun is the only deadly implement you might carry. And nobody is around to tell you how to carry it.