Begin to date vacuous upper-class twit? (3,3)
I believe the answer is:
set off
'begin' is the definition.
(to set off is to begin a journey)
'date vacuous upper-class twit?' is the wordplay.
'date' becomes 'see' (synonyms).
'vacuous' means to remove the middle letters.
'upper-class twit?' becomes 'toff' (term for an upper-class person).
'see' with its middle removed is 'se'.
'se'+'toff'='SET-OFF'
'to' is the link.
(Other definitions for set off that I've seen before include "contrast" , "Start journey or detonate bomb" , "Commence journey or explode bomb" , "Begin journey or explode bomb" , "Begin journey or detonate bomb" .)