reitw is an abbreviation.
Useage 1) reitw is used here when a situation is really difficult or has upset the user. He/she uses it as an expression of extreme disappointment.

Useage 2) reitw is used in this instance as an expression of empowering the self. when a situation arises that the individual needs to over achieve, maybe get the better of a group of persons, they may use reitw.

As this is a new word other useages are sure to be discovered.