Being stupid I upset Anne (5)
I believe the answer is:
inane
'being stupid' is the definition.
(I've seen this before)
'i upset anne' is the wordplay.
'upset' indicates an anagram.
'anne' anagrammed gives 'nane'.
'i'+'nane'='INANE'
(Other definitions for inane that I've seen before include "Annie (anag.)" , "Idiotic" , "Fatuous, mindless" , "Thick" , "Fatuous, vacuous" .)