There is an adage that says over familiarity brings about insult. When you become too familiar with someone or a group of people, knowingly or unknowingly you tend to loose ethics in your relationship with them. Both parties might be unaware of the changes going on around them until there is a dispute.
Remember the saying: too much of everything is bad..so is familiarity. It can rid you of ethics in your relationships.
Familiarity can make one loose respect : the respect you do not give won't be given to you. Familiarity in this context means to know someone to the point you loose respect for that person.
Some instances of familiarity
When you use privilege without asking anymore
When you no longer say thank you to someone
When you enter a room or house without knocking.