Street smart men, what would your advice be to someone growing up in a sheltered area?

My boyfriend is from the Belgian countryside and doesn't seem to have metabolized the idea that peaople are kinda dangerous. He doesn't know how to read the vibe of a bloc and will sometimes do things like:
open his wallet in the middle of the street and show me how much money he has when I asked if he had cash on him
or
want to hold hands and be sweet when we have stumbled upon a clearly sketchy area and what we should be doing is getting the hell out of there.
among other things
I'm not even from a sketchy part of town, I was just raised in Mexico City in the 90's. it's kind of second nature to me to be mindful of my surroundings, so other than my standard reaction of what the hell are you doing, put your phone back in your pocket, close your face and look like youre going somewhere, I don't really know what to tell him.
I'm wondering if there's someone who would be better at verbalizing advice than I am. We're going to be moving to Brussels and while I don't think it's necessarily more dangerous than DF, I'm honestly worried that this will end with him getting mugged in broad daylight


Source.