Scatter most of the crumbs (7)
I believe the answer is:
strewth
'crumbs' is the definition.
(both can be expressions of annoyance)
'scatter most of the' is the wordplay.
'scatter' becomes 'strew' (I've seen this before).
'most of' means to remove the last letter.
'the' with its last letter removed is 'th'.
'strew'+'th'=''STREWTH'
(Other definitions for strewth that I've seen before include "Exclamation of surprise" , "mild oath" , "Aussie exclamation" , "Antipodean exclamation" , "Expression of surprise" .)