Literally means "If I were you".
IIWY, I would add that phrase into Urban Dictionary before someone else takes the credit.
Acronym for "It is what it is".
Accepting things for the way they are regardless of the situation.
Guy 1: Man we messed up so bad this time we'll never get out of it!
Guy 2: Whatta ya gonna do...iiwis.
Guy 1: no doubt