In "Gift of Fear" Gavin de Becker writes that there are multiple behaviours, which verbally signal that an individual may become violent.
Here are some of them:
Forced teaming. This is when an individual starts referring to himself and you as "we" despite you not offering or consenting to becoming a "we" with him. A famous example is "We the people...".
Charm and niceness. "He was so nice" is a very common description given by a victim about perpetrator's behaviour before the attack.
Giving too many details. When people say the truth, they feel no need to back it with additional details.
Typecasting. This means verbal lowering of the social status of someone else through targeting their insecurity in a subtle way. It must appear to have been done incidentally, must be polite, and the edge must appear unnoticed by the attacker.
Labelling is also a form of typecasting.
The purpose of typecasting is to get the victim to try to refute or live up to the label by behaving in a certain way. For example telling someone that "sometimes it is important to read between the lines" implies that the other person does not have the ability to understand the context of a conversation and can make them prove that it is not the case.
Interestingly typecasting is recommended as a pick up tool by the pick up artist Mystery. He calls it "negging".
Typecasting is also hailed in "How to win friends and influence people" as motivational tool. The author Dale Carnegie advises to "give the other person a fine reputation to live up to".
Loan sharking and unsolicited promise. Offering help which comes with explicit or implicit strings attached.
Discounting the word "no". A person who lets his "no" being discarded passes the test for a good victim. This process is called "an interview". This is one way in which victims are selected by process predators.
Mental inflexibility. A person can find it hard to adapt to changing circumstances or people. They can be attached to an idea in a rigid way or they can see themselves as lonely crusades of a cause.
Dark humour. Humour often reveals deep mental attitudes towards the world and people's true concerns. So dark humour can be a sign of a dark personality.
Hopelessness. Pessimism is a predictor of problems, including violence.
So how do these verbal signs fare as predictors of violence in real live?
The analysis of just the first 60 seconds of a random David Cameron's (prime minister of Britain) speech shows how common these violence signals are in the language of politicians.
00:00 -- forced teaming in the title "Let us deal with debt"
00:00 -- charm and niceness, this goes without saying.
00:12 -- forced teaming again
00:18 -- typecasting x7
00:44 -- loan sharking and unsolicited promise x2 or x4, depending how you count it
So to be fair to them, they do warn people of their traits. Unfortunately most people have the tragic ability to ignore these signals.