When I was 18 I learned to stay away from drunken strangers.
Not just drunken strangers — ALL strangers. The Godfather’s point is that you should assume EVERY stranger is dangerous because you just don’t have the requisite info to say otherwise. (In fact, many psychopaths/sociopaths appear “normal”.)
That’s a very good lesson to learn!
I also learned at that age (the hard way) not to BE drunk when fighting with anyone!