The purpose of de-escalation tactics is to bring his anger down, and his ego up a bit. This, accompanied by the correct type of "stance" is key in the ability to defuse the potential fight, or strike first and hard, and with no telegraphing.
The de-escalation stance you want to adopt is one where you hold your palms up in front of your chest, have your feet at about a 45 degree angle, and your weight evenly distributed, knees slightly bent. The purpose of the stance is not to look like a "stance" at all. You should look diplomatic, not threatening. If your de-escalation stance is seen as threatening, you will most of the time up the fight to the next stage. The physical stage.
A lot of this information can be seen at Sammy Franco's site, or Richard Dimitris as well. Demi Barbito also does it.
The reason for the de-escalation stance is that
1. The hand positions give off a body language of peace and diplomacy while keeping your head and body protected from potential sucker blows, etc.
2. It gives you the ability to launch a first strike with non-telegraphing, and maximum power
3. It provides a crucial element of surprise if you decide to launch the first strike.
Cues to look for in deciding that violence is imminent.
If the assaulter's face changes color, grows pale, etc.
If the assaulter begins to stare through you, doesn't respond to anything you say, etc.
If the assaulter is maneuvering you into a corner, dark area, etc.
If the assaulter appears non responsive, incoherent, "high", etc.
There's many other cues, and a great deal of info more, but unfortunately I've got to get going for now
So I'll be back if you want more.
Ryu