Sick of alternative theatre when rude (5,3,7)
I believe the answer is:
under the weather
'sick' is the definition.
(thesaurus)
'alternative theatre when rude' is the wordplay.
'alternative' is an anagram indicator.
'theatre'+'when'+'rude'='theatrewhenrude'
'theatrewhenrude' with letters rearranged gives 'UNDER THE WEATHER'.
'of' acts as a link.
(Other definitions for under the weather that I've seen before include "not so good" , "Depressed" , "Seedy" , "put umbrellas up here?" , "Indisposed" .)