We generally use modifiers such as "so" and "very" for gradable/normal adjectives (water can be quite/so/very HOT, but not quite/so/very BOILING (an ungradable/extreme adjective). Yet would you say the following sentences--which, I'd say, are quite commonplace in colloquial speech--are grammatically incorrect?
You told the teacher I'd been cheating? You're SO dead! ("Dead", obviously, is ungradable.)
Simon Cowell was seen with his VERY pregnant girlfriend. (A woman is either pregnant or not--it can't be graded.)