Real mess (9)
(Another definition for maresnest that I've seen is " messy place".)
'real mess' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for snafu that I've seen before include "Chaos (US slang)" , "in a bad state" , "confused activity" , "Slangy acronym meaning in total confusion" , "Bloomer" .)