Tyrant. When do we use that word.

It just hit me yesterday.  Notice how the word tyrant is used in social media.  I notice that tyrant is only used against rulers who are opposed to the US.  Allies of the US among the tyrants of the world are rarely if ever called "tyrants".  Notice that Gulf tyrants are never called tyrants by Western media or even academia.  And the label can change. Qadhdhafi was a tyrant until he reached agreement with the Bush administration.  The terminology changed as soon as Bush announced from the White House his agreement with "president Qadhdhafi".