Forget it's a way to bid at auction with reserve (2,4)
I believe the answer is:
no dice
'forget it's' is the definition.
(both can be used to reject a request)
'a way to bid at auction with reserve' is the wordplay.
'a way to bid at auction' becomes 'nod' (bidders at auction might nod to place a bid).
'with' says to put letters next to each other.
'reserve' becomes 'ice' (both can mean aloofness).
'nod'+'ice'='NO DICE'
(Other definitions for no dice that I've seen before include "indicates lack of success" , "Emphatic refusal" , "Absolutely not" , "with which many games are unplayable" , "a negative response" .)