These two situations aren't analogous. In 'bored to death' and 'sick to death' the phrase isn't literal - when we say these things we aren't actually going to die. As such, these phrases have developed as colloquial phrases that make sense because speakers have given them meaning, not because they make sense grammatically. When you say 'thirsty to death' you are trying to say something literal which doesn't have the historial usage behind it and therefore you need to stick to the grammatical rules more closely in order for your sentence to make sense.

Hello, Dolco. No, "thirsty to death" is not a commonly used English expression, I've actually never heard it used before. You could say, "I'm dying of thirst." which would have the same meaning. I hope this helps!

Is "I am thirsty to death " ungrammatical? Dolco: Your sentence is perfectly grammatical. As you suspect from the counterexamples, the reason it’s wrong has nothing to do with grammar (or even semantics). For example, we do indeed say “starving to death” (both literally and hyperbolically), scared to death, etc.

@Cara Kramer Thank you so much!! :D

Actually, in the sentence "I'm bored to death" , bored is an adjective. (and yes, "sick" is also an adjective in "I'm sick to death")- they are each describing how "I" feel. There are many adjectives that cannot be used with "____to death". You'll just have to remember that "thirsty to death " is not something we say in English (even though "thirsty" is an adjective). Strangely, we do NOT say "I'm hungry to death"....but we do say "I'm starving to death".......Hmmm