Originally Posted by
Serenidad 
Usually when someone treats me poorly for no reason...it makes me angry....and I drink!
When it's
truly for no reason, its an example of a psychological defense mechanism called "displacement". In your example, it is a psychological process that shifts aggressive impulses to a more acceptable or less threatening target.
This is what happens when the boss yells at the employee who returns home and yells at their spouse, who then yells at their child who in turn kicks the dog.
If it's truly for no reason then do your best not to take it personally. Many times I have found that pointing out the unfairness of a persons actions in these situations leads to an immediate (or at least eventual) apology.