It's obvious I don't think casual dreams need interpretation (2,5,2,3)
I believe the answer is:
as clear as mud
'it's obvious i don't think' is the definition.
('as clear as mud' sarcastically means unclear)
'casual dreams need interpretation' is the wordplay.
'need interpretation' indicates an anagram (letters must be re-interpreted).
'casual'+'dreams'='casualdreams'
'casualdreams' is an anagram of 'AS CLEAR AS MUD'.
(Other definitions for as clear as mud that I've seen before include "Completely unfathomable" , "Totally obscure!" , "hard to follow" , "Not at all easy to understand" .)