Liars

Fool me once, shame on you. 
Fool me twice, shame on me. 
Fool me three times – why are you still on the list of people whose calls I return? 

If someone is consistently unreliable, or tells you things that aren’t true, or says one thing to you and another thing to someone else in order to protect themselves….cut them loose. Liars are the worst. 

Liars can create honest-to-goodness legal and moral problems.
The great thing to realize is that you actually have the power to do this.  You don’t need have to these people in your life.  You can kindly but firmly minimize your interactions with them.  And that frees you up to invite wonderful people into your life.