Ignore this stupid speculating (10)
I believe the answer is:
theorising
'speculating' is the definition.
('theorise' can be a synonym of 'speculate')
'ignore this stupid' is the wordplay.
'stupid' is an anagram indicator (in a stupid order).
'ignore'+'this'='ignorethis'
'ignorethis' with letters rearranged gives 'THEORISING'.
(Other definitions for theorising that I've seen before include "coming up with ideas?" , "indulging in speculation" , "In speculative activity" .)