"I.K.I." is an acronym for the phrase "I Knew It". This is used to call out somebody for subconsciously saying something that's gay, although that person doesn't realize it when they say it.
Sintex: "Yo Shadi, I can't get any smoke out of this blunt, I think you fucked it up when you rolled it."
Shadi: "You gotta suck on it hard, so it comes in your mouth."
Sintex: "I knew it. You said suck on it hard and it'll cum in your mouth. IKI dude."