There are 3 aspects to being intimidating (from what I can gather):
1 – Being capable (and looking it – physique, gun in hands, steady gaze) (look at the dog – any doubts as to who would win?). Ever try catch a feral kitten? I have, and I was terrified of the little fuzzball because I knew how much it was going to hurt to grab it with my bare hands.
2 – Being willing (does the dog look anything other than calm, confident in its abilities, and like you are nothing more than a speck on the sidewalk as far as it’s concerned?). Are you holding a gun in your hands (capable) but your finger is off the trigger and you’re pointing it at the floor and trembling and keep trying to point at the guy but keep dropping back down to low ready?
3 – Restraint. You not only can shoot the man in front of you, but you really, really want to. But you aren’t. You are holding you back, but not by much. His safety lies in your good grace and his ability to not move and obey all instructions immediately. Picture the dog in the picture straining against its leash to come and kill you. You need to be mentally holding yourself back, just waiting for him to take one step closer, or move his hand anywhere near his waist. It is better (for your safety and that of your family) to be mentally restraining yourself from killing him, then to be reluctant and mentally egging yourself on.
You won’t rise to the occasion, you’ll default to your level of training. If you have to force yourself to confront the man in your house, or the men the street trying to push your girlfriend into a car, then your level of training is most likely reluctance. This is a mental barrier to cross, and fortunately mental work can get you most of the way.
At this point you should read Gunpoint Dialogue.