Contemptuous of tips demonstrated in standard letter (10)
I believe the answer is:
dismissive
'contemptuous' is the definition.
(I've seen this before)
'tips demonstrated in standard letter' is the wordplay.
'tips' suggests taking the first letters (I've seen 'tip of' mean this).
'letter' becomes 'missive' (synonyms).
The initial letters of 'demonstrated in standard' is 'dis'.
'dis'+'missive'='DISMISSIVE'
'of' is the link.
(Other definitions for dismissive that I've seen before include "sneering?" , "Disdainful" , "rebuffing me?" , "contemptuous" .)