Meaning 'It's all bullshit'
Coming from the 2005 film 'Dirty Deeds' which says 'IAB'
IABS is a clearer way of saying Its all bullshit
because IAB could mean 'I am bored'
Person one: "Dude! i heard your girlfriend fucked tom last night!!"
Person two: "Na man, IABS, She was with me the whole time"