We sat around? Rubbish! (5)
I believe the answer is:
waste
'rubbish' is the definition.
(I know that rubbish can be written as waste)
'we sat around?' is the wordplay.
'around?' is an anagram indicator (I've seen 'around' mean this).
'we'+'sat'='wesat'
'wesat' with letters rearranged gives 'WASTE'.
(Other definitions for waste that I've seen before include "Rubbish, barren land" , "Useless leftovers" , "Spend to no purpose" , "Detritus" , "Not use effectively" .)