Disorder in communal dining room (4)
I believe the answer is:
mess
This clue is a double definition.
'disorder' is the first definition.
(messing is a kind of disordering)
'communal dining room' is the second definition.
(eg in the army)
'in' is the link.
(Other definitions for mess that I've seen before include "dog's dinner" , "sloppy > food" , "Jumble" , "Where officers eat" , "dirty and unpleasant" .)