If you're saying "im cooked", you're saying "nah bro im dead". This phrase is usually used when someone is in trouble, or some bad situation. Sometimes it can be used for when you're exhausted.
"Nah bro we have a test today?! Shii, im cooked!! I didn't practice at all dawg! Ight, im finna cheat"
when you try studying for an exam but you know you're cooked, so you end up sitting there just looking at your book without even doing any studying (you have sat there for the last 8 hours straight and done no actual work)
(its over for you)
did you study for the finals tomorrow?
i tried but got the im cooked syndrome
damn bro you'recooked